1
The Head, Neck, and Vertebral Column

Learning Objectives

• Identify the main bones and some of their palpable features on the bovine skull. Examples of important features include the temporal line, lacrimal bulla, zygomatic arch, facial tuberosity, nasoincisive notch, foramen orbitorotundum, optic canal, supraorbital foramen, infraorbital foramen, mandibular foramen, mental foramen, and body of the mandible.
• Identify the features of the most clinically important frontal and maxillary sinuses. Know the compartments of the frontal sinus (2-3 rostral and 1 caudal). Study the diverticuli of the caudal compartment of the frontal sinus (cornual, nuchal, and postorbital). Note the dividing thin bony septa of the frontal sinus (transverse oblique and median septum). Identify the lacrimal bulla, the most caudal extent of the maxillary sinus. This sinus can be accessed by drilling a hole through the frontal sinus (see Box 1.1). In dehorning operations in goats, you should keep in mind the superficial location and shallow depth of the frontal sinus at the base of the horn.
• Be able to recall the dental formula and methods for estimating age of cattle and goats using eruption times and changes in the occlusal surface of lower incisor teeth. Know that the incisor and canine teeth in the upper jaw are absent and are replaced by a fibrous structure known as the dental pad.
• Identify clinically important superficial structures on lateral head views (cornual nerve, supraorbital nerve, infraorbital nerve, mental nerve, and dorsal and ventral buccal and auriculopalpebral branches of the facial nerve). Clinically important vessels include the frontal vein, the facial artery (pulse in cattle), and transverse facial artery (pulse in goats). In the neck, identify the external jugular vein, superficial cervical lymph nodes, accessory and great auricular nerves, and parts of the nuchal ligament.
• Identify nerve and blood supply to the horns. You should know the difference in nerve supply of the horn in small and large ruminants, and which nerve or nerves to block in dehorning operations. Note the differences in location and direction of the horn in small and large ruminants. Understand that dehorning is best carried out when the animal is 1-2 weeks of age. Know the meaning of the term epiceras.
• Identify clinically important structures on a median plane of the head (lingual torus and lingual fossa, nasal conchae, medial retropharyngeal lymph node, and other oral, pharyngeal, and laryngeal structures on your laboratory ID list).
• Describe some of the methods and structures associated with enucleation (removal) of the eye that has cancer (i.e., retrobulbar and Peterson's nerve blocks).
• Identify lymph nodes of the head (parotid, mandibular, and lateral and medial retropharyngeal lymph nodes). In the neck, identify the superficial and deep cervical lymph nodes. Know that the lateral retropharyngeal lymph node is the major collection center for lymph from the ruminant head. Understand that the medial and lateral retropharyngeal lymph nodes are incised and examined in meat inspection. You should also know the drainage area for each node.
• Identify major salivary glands of the head (parotid, mandibular, and sublingual).
• Identify neck muscles that form the dorsal and ventral boundaries for the jugular groove (or furrow). Know the difference between jugular groove muscular boundaries in cattle, goats, and sheep. Sheep have a less distinct jugular furrow because of the absence of the sternomandibularis muscle. This muscle forms the ventral boundary in cattle and goats. It is also called the sternozygomaticus muscle in goats.
• Recall the vertebral formula for large and small ruminants. Know vertebral locations for epidural anesthesia in cattle.
• At the end of the head and neck sections watch Videos 1 to 8.

1.1 Skull

Goal: With the help of Figures 1.1-1.9, study the main features of the bovine and caprine skulls on dorsal, lateral, caudal, and ventral views. You should place emphasis on the main paranasal sinuses and bony landmarks for blocking clinically important nerves of the head (e.g., temporal line [cornual nerve], zygomatic arch [auriculopalpebral nerve], infraorbital and mental foramina [infraorbital and mental nerves, respectively], and foramen orbitorotundum [oculomotor, trochlear, ophthalmic, and abducent nerves]). Consult Boxes 1.2-1.5 for clinical application related to features of the skull.

Before you start your dissection of the head, study the bovine skull. Make comparisons with goat and sheep skulls whenever indicated.

The skull is part of the axial skeleton. In addition to the skull, the axial skeleton includes bones of the vertebral column, ribs, and the sternum.

The functions of the skull include protection of the brain, sensory organs, and the upper gastrointestinal and respiratory tracts.

The mandibles and the hyoid apparatus articulate with the skull but are technically not part of the skull. However, they will be studied with the bones of the skull.

The most striking features of the adult bovine skull are the flattened dorsum (frontal bone), the presence of the cornual process (the bony part of the horn), facial tuberosity (a bony prominence on the lateral surface of the maxilla), and the lack of upper incisor teeth and their replacement with the dental pad in the live animal.

The dorsum of the skull in goats and sheep is slightly dome-shaped compared with the flat frontal bone in adult cattle. However, in young calves, the skull is dome-shaped, like the skull in small ruminants.

Look at the dorsal view of the bovine skull and, with the help of Figures 1.1 and 1.2, study the following bones and features: frontal bone, cornual process of the frontal bone (if present in your specimen), lacrimal bone, nasal bone, incisive bone, nasoincisive notch, intercornual protuberance, supraorbital groove, and supraorbital foramen.

Figure 1.1 Bovine skull: caudodorsal view. The epidermal part of the horn (horn sheath or capsule) and the bony part (cornual process) form the horn. Akin to the hoof, the horn sheath and the cornual process are glued together by dermal tissue that contains blood vessels and nerve endings of the cornual nerve and artery. The cornual process and the horn capsule are removed in dehorning operations.

Figure 1.2 A polled (no horns present) bovine skull: dorsal view. Dotted line shows the location of right supraorbital groove. In the live animal, the supraorbital groove houses the supraorbital vein (called the frontal vein after passing through the supraorbital foramen). The bovid may have multiple supraorbital foramina (single in small ruminants).

Study the nerves passing through some of the foramina listed on your laboratory ID list (Table 1.1).

Note that the cornual process in cattle lies several centimeters caudal to the eye or bony orbit. It extends in lateral and dorsal directions (Figure 1.1). In goats, it lies relatively close to the caudal border of the eye and extends in a caudal rather than lateral direction (Figure 1.3).

Table 1.1 Major foramina of the bovine skull and nerves passing through them. Understand that there are vessels that accompany these nerves (not listed). CN V1, ophthalmic subdivision of CN V; CN V2, maxillary subdivision of CN V.

Box 1.1

Drilling a circular hole in the skull or other bones is known as trephination. This hole is generally made to drain inflammatory exudate and flush sinuses in the skull with antiseptic solution. Diseases of the frontal sinus result from microbial infections mostly from dehorning operations in cattle. Consult Figure 1.9d.

Box 1.2

In the bovine, the supraorbital groove is palpable. It houses the...