Part 5

Description.—The zygomatic is small, slender, rod-shaped, and forms the lateral portion of the upper jaw. The anterior portion of the zygomatic represents the jugal and is fused with the maxilla and with the anterior processus maxillaris of the nasal bone, the maxilla, and the posterior portion, the quadrato-jugal, which articulates with the quadrate bone.

=The Vomer.= Location.—The vomer is located in the median nasal septum. It articulates with the rostrum of the sphenoid, being connected to it by a mass of ligaments. It touches anteriorly the posterior portion of the maxilla.

Description.—The vomer is a median bone and aids in the formation of the septum nasi. It consists of a thin plate, thickest posteriorly and diminishing toward the anterior edge.

=The Jugal and Quadrato-jugal.=—The jugal and quadrato-jugal are united forming a long slender cylindrical bone called the zygomatic, lying at the outer side of the upper jaw. They have been described under zygomatic, which see.

=The Quadrate.= Location.—The quadrate bones, or ossa quadrata, two in number, are located antero-laterally to the temporal bones. Each articulates inferiorly with the posterior articular portion, or pars articulare, of the inferior maxilla and infero-laterally with the quadrato-jugalare portion of the zygomatic. It articulates antero-internally with the pterygoid and supero-posteriorly with the temporal.

Description.—The quadrate bone is anvil-like in shape. It has an anterior process, the orbital process, for muscular attachments, and posteriorly it affords attachment to the ear drum.

=The Inferior Maxilla.= Location.—The inferior maxilla, lower jaw, or os maxillare inferius, also called the mandibular bone, or pars dentis, is analogous to the lower jaw of mammals. It articulates posteriorly with the quadrate bone.

Description.—The inferior maxilla is the largest bone of the face. It is made up of a right and a left limb which are separate in the fetus and which unite subsequently anteriorly, forming the inferior portion of the beak. Each limb of the jaw is developed from five elements: the pars articularis, which forms the jaw-joint and, expanded, articulates with the quadrate bone; the pars angularis, lying just in front of the pars articularis; the pars supra-angularis, a slender bone lying just above the angularis; the splenial, a thin plate of bone, lying along the inner surface of the mandible; and the pars dentalis, which forms the anterior portion of the jaw.

=The Turbinate Bones.= Location.—The turbinate bones, or ossa turbinata, six in number, are attached to the lateral walls of the nasal cavity (Fig. 26, No. A, 1 and 2). In each nasal cavity there are three turbinate bones, one anterior and two posterior. Of the two posterior the upper one lies supero-posterior to the inferior one. The turbinate bones are attached to the lateral nasal walls, project into the cavity and thus greatly diminishing its extent.

Description.—Each turbinate bone is composed of a very thin lamina, finely cribriform in many places, and in the fresh state, covered on both sides with mucous membrane. These bones are curled and partly membrano-cartilaginous structures which give greater surface in the nasal passage for mucous membrane in which the olfactory nerve terminal filaments are distributed.

=The Nasal Cavity.=—The nasal cavity, or cavum nasi, is a longitudinal passage which extends through the upper part of the face. It is divided into right and left halves by a median septum nasi. Its walls are made up of the premaxilla, maxilla, nasal, vomer, and palatine bones.

=The Hyoid Bone.= Location.—The hyoid bone, or os hyoideum, is situated chiefly between the rami of the mandible, but its upper part extends around the outer margin of the base of the skull. The hyoid bone does not articulate with any bones of the skull, but is firmly attached by strong fibrous structure.

Description.—The hyoid bone consists of the following parts: the body, or basi-hyal, which is subcylindrical and presents in front a trochlear articular surface, convex transversely, and concave vertically for articulation with the ewer-shaped portion of the glosso-hyal. The anterior free portion, or lingual process, is called the glosso-hyal, or entoglossal bone. The lingual process gives support to the muscular and fibrous structures of the tongue. On either side of the basi-hyal there is a limb passing posteriorly along the side of the superior larynx, extending upward along the outer border of the occipital bone. This is the cornu of the os hyoideum and is divided into two elements, first, the basi-branchial which is bone and articulates with the basi-hyal, and the second, the cerato-branchial, cartilaginous in structure. In the center and projecting backward from the body of the os hyoideum is a spur process called the uro-hyal, partly bony and partly cartilaginous, and which rests upon the superior larynx.

THE VERTEBRAL COLUMN

The vertebral, or spinal column consists of 42 bones, as shown in the following table:

Cervical region 14 Dorsal region 7 Lumbo-sacral region 14 Coccygeal region 7 —— Total 42

Many of the bones of the dorsal and lumbo-sacral regions do not have free articulations. The cervical and coccygeal alone have free movements.

=The Cervical Vertebræ= (Fig. 4, No. 59; Fig. 5, Part II, No. 2). Location.—The cervical vertebræ form the neck of the fowl.

FIG. 9.—Os hyoidum and tongue muscles. 1, Glosso-hyal. 3, Basi-hyal. 4, Basi-branchial element of the cornua. 5, Cerato-branchial element of the cornua. 6, Uro-hyal or spur process. 7, Genio-hyoideus. 8, Cerato-hyoideus showing the slender tendon. 9, Hyoideus transversus. 10, Hyoideus transversus. ]

Description.—The long cervical section of the spinal column is S-shaped and is made up of fourteen vertebræ. The anterior segments move freely forward, the middle ones backward and the posterior ones forward, allowing the S-shaped curve of the neck. The neck is flexible so that it is possible for the beak to reach the coccygeal oil gland. The bird is enabled to reach the feathers on all parts of the body to cleanse and oil them.

=The Atlas.= Location.—The first cervical vertebra is called the atlas. Anteriorly it articulates with the single condyle of the occipital bone. Posteriorly it articulates with the axis, or second cervical vertebra.

Description.—The atlas is the smallest of the cervical vertebræ and is ring-shaped. The anterior articular surface, half-moon in shape, forms a deep articular cavity. The joint, called a ball-and-socket joint, makes possible movements in all directions. The condyle of the occiput also touches an articular end of the odontoid process of the axis, or second cervical vertebra. Posteriorly there projects from the atlas two small lateral wings possessing articular facets which articulate with similar facets on the lateral wings of the axis. Posteriorly the body of the atlas is also provided with an articular surface which articulates with a similar surface on the anterior portion of the body of the axis.

=The Axis.= Location.—The axis is the second cervical vertebra. It articulates anteriorly with the atlas, and by a facet on the extreme anterior end of the odontoid process, with the condyle of the occipital bone. Posteriorly it articulates with the third cervical vertebra.

Description.—The body of the axis is short. The upper anterior portion of the body of the axis is provided with a tooth-like process called the odontoid process. There are two anterior lateral wings provided with small articular facets which articulate with similar facets of the atlas. The anterior surface of the body of the axis forms a true articulation with the body of the atlas.

The axis is provided with a superior and an inferior spine. There are two posterior articular processes which articulate with the prezygapophyses, or anterior articular processes, of the third cervical vertebra. The posterior part of the body of the axis forms a true articulation with the body of the third cervical vertebra.

=Other Cervical Vertebræ.=—Beginning with the axis, the body of which is relatively short, the body of each succeeding vertebra is longer than that of the preceding. The articulations of each vertebra with adjoining vertebræ are effected by means of diarthrodial facets, convex in one direction and concave in the other.

FIG. 10.—A. Diagram of three first dorsal vertebræ and scapular arch-side view. B. Diagram of section through the hemal arch.

A. 1, First dorsal segment. 2, Second. 3, Third. 4 and 5, Hemal arches. 6, The pleurapophyses or floating ribs. 7, The third pleurapophyses or dorsal vertebral rib articulating with the hemapophysis or sternal rib, 8, and this in turn with the wing of the sternum form a hemal arch. 9, The sternum. 10, Intervertebral foramen through which the nerves pass. 11, Articulation with the body of vertebra parapophyses. 12, Articulation with transverse process or diapophyses. 13, Oblique process or zygapophysis. 14, The epipleural appendage.