FACIAL ANGLE. VERTEBRAL COLUMN. RIBS. STERNUM. 489 



The prominence of the facial part of the skull also varies 

 greatly. It may be said, speaking generally, to vary inversely 

 with the development of the intellectual faculties. The condition 

 of the skull in this respect is expressed by reference to the cranio- 

 facial angle, which is the angle between the basicranial axis, i.e. 

 the line drawn from a point midway between the occipital con- 

 dyles through the median plane of the skull to the junction be- 

 tween the ethmoid and presphenoid, and the facial axis, i.e. the 

 line drawn from the anterior end of the premaxilla to the an- 

 terior end of the basicranial axis. When the face projects straight 

 out in front of the cranium this angle is nearly 180°, i.e. the two 

 axes are nearly in the same straight line ; when on the other 

 hand the face lies below the anterior end of the cranium it is less 

 and in man approaches a right angle. The first condition, viz. 

 that of projecting face and large facial angle, is known as frog- 

 nathism,the other condition, in which the facial angle is smaller, 

 is called orthognathism. 



The hyoid bone is reduced to a transverse bar (body) carrying 

 two pairs of cornua. 



The vertebral column, except in the Cetacea, is divided into . 



five regions, viz. cervical, thoracic, lumber, sacral and caudal ^/ 

 (Fig. 261). In the aquatic Cetacea, which are without hind 

 limbs, the lumbar region passes gradually into the caudal ; on 

 the other hand the cervical region is strikingly shortened, and 

 the fusion of its anterior vertebrae renders it rigid and immove- 

 able. The vertebral bodies are only exceptionally (neck of 

 Ungulates) connected by articular surfaces, but are usually 

 joined by elastic discs (intervertebral ligaments). The first 

 cervical vertebra (atlas) is a bony ring with broad, wing-like, 

 transverse processes. The axis has an odontoid process. The 

 dorsal vertebrae are characterised by high, crest-like, spinous 

 processes, and by the possession of ribs. The anterior ribs are 

 attached by cartilage to the sternum, which is usually elongated 

 and composed of a number of bony pieces arranged one behind 

 another ; the posterior ribs (the so-called " false ribs ") do not 

 reach the sternum. The ribs articulate with the vertebrae by 

 means of a capitulum and tuberculum. The first piece of the 

 sternum, which is sometimes keeled (bats, moles, etc.), is called 

 the manubrium ; the last piece is called, as in the lower types, 

 the xiphoid process or ensiform cartilage. In monotremes alone 



