The skull is divided into the cranial and facial portions. In these parts we find present 31 bones: one occipital, two parietal, two frontal, one ethmoid, one sphenoid, and two temporal; all of which constitute the cranial group; two premaxillary, two maxillæ, two nasal, two lacrimal, two palatine, two pterygoid, two zygomatic, one vomeral, the two jugal, and two quadrato-jugal, which constitute the facial group; two quadrati and one inferior maxillary, which constitute the inferior jaw group. The peculiarities of the skull are the long os incisivum and the single condyle located on the occipital bone just below the foramen magnum. The condyle articulates with the atlas. The head of the bird is small in proportion to the size of the body, and in front it is conical in shape. THE CRANIUM The cranial cavity, or cavum cranii, incloses the brain with its membranes and vessels. The dorsal wall, or roof, is formed by the frontal and the parietal bones. In the median line of the cerebral portion is the internal parietal crest. The roof of the cerebellar portion is marked centrally by a groove. The posterior wall of the cerebellum is formed by the occipital bone. The lateral wall is formed chiefly by the temporal bone. It is marked by a ridge which divides the cavity into the cerebral and cerebellar compartments. The cerebral portion is marked by a depression which receives the optic lobes. A crest divides this cavity from the optic portion. The walls are marked by digitations and vascular grooves. [Illustration: FIG. 4.—The skeleton of the domestic fowl. 1, Os incisivum. 2, External nasal opening. 3, Os nasale. 4, Os lachrymale. 5, Lamina perpendicularis. 6, Os dentale. 7, Os palatine. 8, Os quadrato-jugal. 9. Os pterygoideum. 10, Os quadratum. 11, Os articulare. 12, External auditory canal. 13, Atlas. 14, Os carpi radiale. 15, Radius. 16, First finger. 17, Os metacarpus. 18, Second finger. 19, Third finger. 20, Os carpi ulnare. 21, Ulna. 22, Humerus. 23, Thoracic vertebræ. 24, Scapula. 25, Os ilium. 26, Foramen ischiadicum. 27, Caudal vertebræ. 28, Pygostyle. 29, Foramen obturatum. 30, Os ischium. 31, Processus uncinatus. 32, Vertebral rib. 33, Os claviculum or furculum. 34, Os coracoideum. 35, Os femoris. 36, Os pubis. 37, Body of sternum. 38, Lateral internal process of sternum. 39, Costal process of sternum. 40, Sternal crest, cristi sterni, or keel of breast-bone. 41, Sternal rib. 42, Lateral external process of sternum. 43, Os fibula. 44, Xyphoid process of sternum. 45, Internal notch. 46, Os patella. 47, Os tibia. 48, Os metatarsus. 49, Second toe. 50, Fourth toe. 51, Os metatarsale. 52, First toe. 53, Second toe. 54, Second phalanx of second finger. 55, Os metacarpus. 56, Air opening in humerus. 57, Hypocledium. 58, External notch. 59, Cervical vertebræ. 60, Foramen oblongum. ]