LEPUS CUNICULUS 283 



the supra-occipital (c), a large median bone joining the parietals in 

 front, the squamosals and periotics at the side and the exoccipitals 

 ventro-laterally, while its mid ventral portion forms part of the wall 

 of the foramen magnum. Its postero-dorsal portion is marked by 

 strong ridges into which are inserted the muscles raising the head. 

 The lateral bones are the exoccipitals (c), which form the major part 

 of the wall of the foramen magnum. They bear posteriorly strong 

 curved smooth ridges, the occipital condyles, which articulate with 

 the condylar facets of the atlas. Laterally each bone is produced 

 downwards as a paroccipital process behind the periotic bone. 

 Between the posterior border of the tympanic bulla and the exocci- 

 pital is an irregular fissure, the foramen lacerum posterius, through 

 which passes the ninth, tenth and eleventh cranial nerves and the 

 internal jugular vein. The twelfth nerve leaves the cranium by two 

 branches which pass through the body of the condyle, and the 

 condylar foramina that transmit them are best seen on the inside 

 of the condyles. The basal part of this ring of bones is completed 

 by a large basioccipital (c) ; it forms the ventral wall of the foramen 

 magnum and contributes a small part of each condyle. 



The lower jaw or mandible (m) consists of a pair of flattened 

 triangular masses of bone, thin and broad posteriorly, but getting 

 thicker and narrower as they pass forward till they finally unite 

 in the symphysis menti. At the anterior end each half or ramus 

 bears a single incisor tooth ; this is followed by a diastema, and this 

 by two premolars and three molars all molarif orm and similar to those 

 in the upper jaw. Each ramus gives off posteriorly a broad, thin 

 ascending coronoid process which passes up to articulate, by means of 

 a transverse expansion of its upper end, with the under side of the 

 zygomatic process of the squamosal. The postero- ventral border of 

 the ramus is known as the angle and its edge is slightly incurved. On 

 the inner side of each ramus just behind and below the last molar 

 tooth is an aperture, the inferior dental foramen, through which a 

 branch of the mandibular nerve enters the bone to supply the teeth. 

 The hyoid bone (c) is a small bone embedded in the muscles 

 of the base of the tongue between the hinder ends of the rami. 

 It possesses a body and two pairs of cornua. The anterior cornua 

 represent the persistent remains of the hyoid arch of the embryo 

 and the posterior cornua, also termed thyrohyals, the lower ends 

 of the first branchial arch. 



Appendicular Skeleton. 



We now pass on to consider the remaining part of the 

 skeleton comprising the pectoral and pelvic girdles and the fore 

 and hind limbs. All of its main bones are cartilage bones save 



