64 



GENERAL ZOOLOGY 



In fishes the hemal rib extends from the side of a centrum of a 

 vertebra into the muscle of the body wall. In the caudal region 

 the ventral ends of the ribs meet in the mid-line to form a hemal 

 arch, enclosing blood vessels (Fig. 38). A caudal vertebra in 

 such a case is provided with a neural arch above the centrum 

 and a hemal arch below. 



The pleural ribs of man are restricted to the thoracic region 

 of the body. The first seven vertebrae are the vertebrae of the 

 neck or cervical region. The next twelve vertebrae belong to 



Fig. 38. — Posterior (A) and side view (B) of a caudal vertebra of a teleost fish, 

 c, centrum; ha, hemal arch; na, neural arch. 



the thorax and it is to the thoracic vertebrae that the dorsal 

 ends of the ribs are articulated at two points, viz., the head and 

 tubercle (Fig. 39). The head or capitulum, at the dorsal end of 

 the rib articulates with a facet on the centrum of the vertebra 

 called the parapophysis. The facet on the centrum may be 

 entirely on a single vertebra, as in Fig. 39, or it may be shared 

 by two adjoining vertebrae. The tubercle or tuberculum of the 

 rib articulates with the diapophysis, a facet in the transverse 

 process of the vertebra. The neck of the rib is the region 

 between the head and the tubercle. The first ten pairs of ribs 

 are connected at their ventral ends by means of costal cartilages 



