28 



The ribs and sternum. 



1. The Ribs, (a) Examine a typical rib (4th or 5th), noting — 



(1) The bony vertebral portion, curved above, nearly straight 



below ; the head of the rib articulating with a facet formed 

 by the centra of two adjacent vertebrae ; the tubercle articu- 

 lating with the transverse process of the vertebra ; and 

 beyond the tubercle, a small projection for the attachment 

 of ligaments. 



(2) The cartilaginous sternal portion, connecting the vertebral 



rib with the sternum. 

 (b) The ribs in general. Note the gradual increase in the length of the 

 ribs from the first to the sixth, and beyond the sixth the gradual 

 shortening : beyond the ninth rib the want of tubercles, and the 

 facets for the head of the ribs confined to one centrum : the sternal 

 portions of the seven first ribs reaching the sternum, those of the 

 eighth and ninth connected with the ribs in front of them : the re- 

 mainder being floating ribs. 



2. The sternum. Observe that it is constituted of the following parts. 



(a) The manubrium or anterior portion, keeled on its ventral 



aspect. 

 (6) The xiphisternum, or posterior portion, long and slender, 



ending behind in a plate of cartilage, 

 (c) Between these, four long portions and one short. 

 Note the position of the facets for the articulation of the ribs, the first on 

 the manubrium, the others between the several sternebrae. 



K. The Skull. 



The cranium proper. For the purposes of study, the cranium may be 

 regarded as composed of certain segments, viz. : — 

 (a) The occipital segment. Note — 



(1) The basi-OCCipital, forming the floor of the hinder end ot the 



cranial cavity, and bounding the foramen magnum in front. 



(2) The ex-occipitals, bounding the foramen magnum laterally, 



and forming the greater part of the condyles. Note, at the 

 outer ?ide of each, the long backwardly directed par-occipital 

 process or paramiistoid, closely applied to the tympanic bulla. 



(3) The supra- occipital, a large median bone, bounding the 



foramen magnum posteriorly. 

 (6) The parietal segment. Note — ■ 



(1) The basi-sphenoid, directly in front of the basi occipital, 



having on its dorsal surface the sella turcica for the lodge- 

 ment of the pituitary body. 



(2) The ali-sphenoids, a pair of wing-like bones fused to the 



sides of the basi-sphenoid, and forming part of the floor of 

 the cranial cavity. From the ventral surface of each there 



