Fig. 2.12 Radiograph of the lower jaw temporary and permanent teeth: dorsoventral view. The deciduous and developing permanent teeth are shown in this radiograph. The deciduous dental formula present by two months of age is:

Replacement begins at about 3 months of age, to be completed by about 7 months, although there is some variation in the timing of tooth eruption depending on breed and size. Premolar 1 (clearly visible) is without a deciduous precursor and erupts between 4 and 5 months.

Fig. 2.13 Radiograph of the mandible: ventrodorsal intraoral view.

Fig. 2.14 Radiograph of the maxilla and nasal chambers: dorsoventral intraoral view. The tooth roots appear foreshortened in this view as they are angled relative to the x-ray beam. The two nasal chambers can be seen without superimposition.

Fig. 2.15 Radiograph of the head: lateral view, dentally immature dog. The developing permanent teeth can be seen within the maxilla and the mandible. The deciduous teeth, including their roots, are slender.

Fig. 2.16 Radiograph of the head: ventrodorsal view, dentally immature dog. The permanent teeth develop medial to their deciduous counterparts and grow out laterally. The suture between the zygomatic process of the temporal bone and the temporal process of the zygomatic bone is visible in this young dog.

Fig. 2.17 Surface features of the eye: left lateral view (1). The eye is shown with eyelids open. The palpable bony orbital margin is completed laterally by an orbital ligament linking the supraorbital process with the zygomatic arch (cf. Fig. 2.39). A dog has quite a wide field of view, in the order of 240°, and there is some measure of overlap between the fields of left and right eyes when it is looking straight ahead.

Fig. 2.18 Surface features of the eye: left lateral view (2). The third eyelid has been exposed by manual pressure exerted through the eyelids. This procedure pushes the eyeball slightly into the orbit compressing intraorbital fat. A normal component of orbital fat is important for holding the eyeball firmly against the inner surfaces of the lids and causing it to protrude a sufficient distance beyond the orbital margin.

Fig. 2.19 Surface features of the ear: left lateral view. The helix of the pinna has been raised and held erect. From the opening visible in the picture the ear canal extends downwards almost vertically and then turns inwards and forwards at 90° towards the eardrum (see also Fig. 2.145 of the head in transverse section). Consequently lateral traction on the pinna will straighten the canal.

Fig. 2.20 Skeletal basis of variation in conformation of the head: dorsal and lateral views. The shape of the head is determined in large measure by the skull, and in particular the facial region. Within the spectrum of skull construction, three broad categories are generally recognized – brachycephalic, mesaticephalic and dolichocephalic. The montage of skulls in the accompanying illustration shows all three categories; e.g. bulldog (brachycephalic), basset hound (mesaticephalic), and rough collie (dolichocephalic). It is the facial part of the skull that is shortened/widened in brachycephalics, but lengthened/narrowed in dolichocephalics. These categories refer specifically to head type and say nothing about the rest of the body. This fact is demonstrated by the three lateral views at the foot of the page – brachycephalic (Pekinese), mesaticephalic (dachshund), and dolichocephalic (Sealyham terrier). The lateral views also show the difference in level between the dorsal contours of the cranium and face. Although in approximately parallel planes, the marked step down from cranial to facial level produces the nasofrontal angle or ‘stop’. In brachycephalic breeds the shortened broadened face is coupled with a deepened stop and eyes that are directed more forwards. Selective breeding has also produced a discrepancy in length between upper and lower jaws – a short face is generally prognathic with an undershot lower jaw: a long face is often accompanied by a brachygnathic, receding lower jaw. The montage also demonstrates the enormous intraspecific size range, especially well displayed by the juxtaposed Chihuahua and Great Dane skulls at the top of the page. The head of a brachycephalic breed (boxer) is also displayed at the top of the page.

Fig. 2.21 Radiograph of the head: lateral view, dolichocephalic breed. The nose is elongated and there is little ‘stop’. The frontal sinus is flattened dorsoventrally.

Fig. 2.22 Radiograph of the head: lateral view, mesaticephalic breed. The nose and cranium comprise equal proportions of the skull.

Fig. 2.23 Radiograph of the head: lateral view, brachycephalic breed. The nose is markedly shortened and there is a pronounced ‘stop’. The frontal sinus is virtually absent. The cranium is domed and the mandible has a convex contour. Mandibular prognathism is present.

Fig. 2.24 Superficial structures of the head and cranial end of the neck: left lateral view. The skin has been removed apart from a narrow rim in the lips, around the nostril and eye, and on the distal part of the scapha of the auricular cartilage. Because the animal was embalmed with jaws open and head bent down slightly on the neck, the fat and fascia on the underside of the ‘throat’ was preserved as a compressed and ‘waterlogged’ mass. In the process of removing this mass the few delicate transverse strands of the sphincter colli superficialis muscle were removed (see Fig. 3.6). The superficial structures of the head are also shown from dorsal view in Figs 2.57 and 2.61, and from ventral view in Fig. 2.125.

Fig. 2.25 Superficial structures of the head after removal of the platysma muscle: left lateral view. Muscle fibers from the dorsal border of the platysma are inter-mingled with those of the intermediate component so that severance of this association on platysma removal has left a ‘ragged’ line on the surface of the intermediate at the area labelled ‘X’ on the drawing. Complete removal of the orbicularis oris muscle is difficult since its fibers intermingle with those of the levator nasolabialis. Some of its place amongst the roots and follicles of the sensory tactile hairs. The mental muscle is infiltrated with fat and fibrous tissue in the mentum and therefore its limits are difficult to define.

Fig. 2.26 Superficial structures of the temporal, auricular, parotid and masseteric regions after removal of the platysma muscle: left lateral view. This is a closer view of part of the dissection shown in Fig. 2.25. Some limited cleaning of superficial fascia from around the concha of the auricular cartilage exposes the parotid salivary gland and the proximal part of its duct. Cutaneous innervation of the head is through the trigeminal nerve (V), some of the branches being displayed in this dissection (see also Fig. 2.58). However, many of its terminal ramifications have been unavoidably removed along with the skin and platysma muscle so that at best only the proximal stumps of such nerves are preserved intact.

Fig. 2.27 Superficial structures of the head after removal of the platysma and sphincter colli profundus muscles: left lateral view. The intermediate component of the sphincter colli profundus and the nasofrontal part of the levator nasolabialis muscle have been removed. The extensive distribution of the facial nerve (VII) to the facial musculature is contrasted with a less apparent distribution of sensory branches of the trigeminal nerve (V). The ramifications of cutaneous nerves are generally removed with the skin. The extensive and pronounced venous drainage in the superficial fascia is in marked contrast to the more restricted distribution of arteries (see also Fig. 2.127).

Fig. 2.28 Superficial structures of the temporal, auricular, parotid and masseteric regions after removal of the platysma and sphincter colli profundus muscles: left lateral view. This is a closer view of a part of the dissection shown in Fig. 2.27. Removal of the intermediate part of the sphincter colli profundus has exposed the mandibular lymph nodes (see also Fig. 2.127). These nodes are of considerable size when compared to the very small parotid lymph node exposed in Fig. 2.30. Lymph nodes are generally few in number and small in size (relative to body size) in the dog and lymphatic tissue is generally poorly displayed. Lymphatic vessels (apart from the thoracic duct – see Chapter 5) are not demonstrated.

Fig. 2.29 Superficial nerves and blood vessels of the head: left lateral view. The zygomatic and zygomaticoauricular muscles, the parotidoauricular muscle in part, and the maxillary component of the levator nasolabialis muscle, have been removed. The ventral end of the parotidoauricular muscle is retained in order to leave intact the cervical branch of the facial nerve (VII) linking with the transverse cervical component of cervical nerve 2 on its surface. The parotid salivary gland has been removed ‘piecemeal’ until only a small component from which the duct originates remains in position.

Fig. 2.30 Superficial nerves and blood vessels of the temporal, auricular, parotid and masseteric regions after removal of the facial muscles and parotid salivary glands: left lateral view. This is a closer view of a part of the dissection shown in Fig. 2.29 but with the parotid salivary gland removed, including the proximal part of its duct, and that component of the superficial temporal vein which lay embedded in parotid gland tissue also removed. The cut ends of the vein are visible as it leaves the temporal fascia dorsal to the zygomatic arch, and just before it enters the maxillary vein caudoventral to the concha of the auricular cartilage. The small parotid lymph node, now uncovered, partially obscures the communicating ramus linking the auriculotemporal branch of the trigeminal nerve (V) with the dorsal buccal branch of the facial nerve (VII).

Fig. 2.31 Auricular cartilages, temporal and masseter muscles after removal of the facial muscles: left lateral view. The remaining facial muscles have been removed along with the mandibular and parotid lymph nodes and the terminal ramifications of the facial nerve (VII). Infraorbital branches of the maxillary nerve (trigeminal V) are now visible extending rostrally from the infraorbital foramen into the muzzle. Slight displacement of the facial vein away from the rostroventral border of the masseter muscle has exposed the deep facial vein, the facial artery and the mylohyoid nerve extension onto the face (see also Fig. 2.98).

Fig. 2.32 Auricular and scutular cartilages after removal of the superficial muscles and parotid salivary gland: left lateral view. This enlarged view of the auricular region (Fig. 2.31) shows scutular and auricular cartilages and some intrinsic auricular muscles.

Fig. 2.33 Auricular cartilage and external acoustic canal following tragic resection: left lateral view. The ear canal is opened to demonstrate its right-angled bend before the external acoustic meatus and tympanic membrane are reached (see also sections, Figs 2.145 and 2.146).

Fig. 2.34 Temporal, parotid, auricular and masseteric regions and the external acoustic canal following removal of the auricular cartilage: left lateral view. The facial nerve (VII) emerges from the stylomastoid foramen caudal to the meatus (see Fig. 2.3) and practically encircles it.

Fig. 2.35 Mandibular ramus and temporal muscle after removal of the masseter muscle and temporal fascia: left lateral view (1). Removal of the auricular and scutular cartilages exposed the stout temporal fascia which was subsequently removed. Some ‘ragged’ areas of the temporal muscle surface show where numerous fibers took origin from the internal face of the temporal fascia itself. Removal of the masseter muscle has involved further cutting back of superficial components of both the trigeminal (V) and facial (VII) nerves. The cut stumps of these nerves are visible above and below the maxillary artery and vein, lateral to the temporomandibular joint.

Fig. 2.36 Mandibular ramus and temporal muscle after removal of the masseter muscle and temporal fascia: left lateral view (2). This is a closer view of the temporal and masseteric regions of the dissection shown in Fig. 2.35. It displays the deep facial vein leaving the pterygopalatine fossa and embedded to some extent in the zygomatic salivary gland. The buccal nerve from the mandibular branch of the trigeminal nerve (V) appears in the cheek immediately rostral to the coronoid process of the mandibular ramus. Caudal to the external acoustic meatus the remains of the caudal auricular vessels and nerve have been displaced caudally after removal of the auricular cartilage. They are spread out on the aponeurosis of the cleidocervical and sterno-occipital muscles in the region of the atlas wing.

Fig. 2.37 Temporal fossa and mandibular ramus after removal of the temporal and masseter muscles: left lateral view. ‘Piecemeal’ removal of the temporal muscle has left its nerve and blood supply intact and visible through the mandibular notch (see also Figs 2.69 and 2.70). In the process of temporal muscle removal the isolation of orbital structures within the periorbita was clearly apparent: temporal fascia fuses with the orbital ligament whereas the temporal muscle itself merely butts onto but does not attach to the periorbita (see also Fig. 2.70). Likewise, separation of the temporal muscle from the maxillary nerve and blood vessels and buccal nerve in the pterygopalatine fossa ventral to it was readily accomplished (see also Fig. 2.72). The hole in the cranium at the point labelled ‘X’ was made to allow the insertion of a hook to support the head following embalming of the cadaver.

Fig. 2.38 Temporal and pterygopalatine fossae after removal of the coronoid process of the mandible: left lateral view. The coronoid process of the mandible has been sawn through and removed, opening the pterygopalatine fossa from a lateral aspect. Fat and fascia were cleaned from around the deep facial vein and the zygomatic salivary gland, and from the underlying buccopharyngeal fascia rostral to the medial pterygoid muscle. A short section of facial vein where it crosses the mandible has also been removed so that the cheek with its muscular basis of buccinator muscle is traceable for a short distance caudally, internal to the mandibular ramus.

Fig. 2.39 Lower jaw after removal of the masseter muscle, ventral part of the cheek and lower lip: left lateral view. The lower jaw (mandible) has been exposed by removing the lower part of the cheek. From the angle of the mouth a cut was made caudally through the buccinator muscle and buccal fascia to the mandibular ramus at the level at which the coronoid process was removed (see Fig. 2.38). The buccinator muscle was cut from the mandible and the buccal mucosa was severed at its line of reflection from the internal surface of the lip and cheek onto the mandible.

Fig. 2.40 Pterygopalatine fossa and lower jaw after removal of the mandible: left lateral view. The remaining part of the left mandible has been removed by: making a vertical saw cut through the mandibular body caudal to lower premolar tooth 2; disarticulating the temporomandibular joint; severing the digastric, medial pterygoid, lateral pterygoid, mylohyoid, geniohyoid and genioglossal muscles at their attachments; cutting the mandibular alveolar vessels and nerve at their entry into the mandibular canal (see Fig. 2.98); severing sublingual mucosa in the floor of the mouth at its line of reflection onto the internal face of the mandible.