598 OSTEOLOGY OF LARID^. 



with tlie sternum; the last one does not, althougli it Las a sternal rib attached to it. 

 Neitlier of them shows traces of posterior ol)li(nie processes. 



Steknuji. — The sicrninn varies more in th(' difl'erent subfamilies than any other por- 

 tion of the slieleton except the skull. It will, therefore, be necessary to institute com- 

 j)arisons bet\\een the four types, although a general description may still be made for 

 either of the groups. I describe it held upside down. 



The body of the bone is pretty regularly rectangular, and about twice as long as 

 broad across the middle. In Les1ridi>t(€.aud Stcrniua' the lateral borders are nearly 

 straight or but slightly concave, while in LaritKv the outline is very concaA'e from the 

 protrusion of the costal processes. This unich greater develoinuent of the costal pro- 

 cesses in LaviiH gives a greater breadth anteriorly, and detracts from the more perfectly 

 rectangular shape which obtains in the other subfamilies. Just i)osterior to the costal 

 processes are the six articulating facets for the sternnl ribs. These are simply linear 

 perpendicular eminences, separated by curved sulci from each other. They extend 

 but little more than half the length of the sternum, the remaining portion of the bor- 

 der being thin and plain. 



The anterior border is verj^ convex, running forward a considerable distance from 

 the costal processes, having on the median line a large semicircular, well-developed 

 mauubrial process. The outer half of this border is thin, corresponding with the costal 

 processes; the inner very thick, and deeply grooved to form the coracoid facets. These 

 facets are of a shape somewhat peculiar, as they curl downward and inward toward 

 each other, to meet on the median line beneath the manubrium, which consequently 

 overhangs them. In the middle of their course they are very shallow, but again, at 

 their outer extremitj', become sulci by means of a short, stout process of bone which 

 overhangs them. 



The posterior border differs in the Lestridhwj from the other subfamilies. It has but 

 a single long, slender incurved process, forming Avith the xiphoid cartilage a single 

 deep oval excavation. In the other subfamilies the outer process is not so long and 

 slender, it projecting but little if any beyond the extremity of the xiphoid; and there 

 is, in addition, a second small, short, slender process midway between the external one 

 and the xiphoid, which divides the single membranous space of the Lcsiridlnw into two 

 small spaces, each of a more or less oval shape. 



The dorsum of the sternum is strongly vaulted, both transversely and longitud- 

 inally. The amount of convexity both ways is greatest in Lestridiiuv, .least in Sierniuai. 

 In Lfsirtdina; also, the convexity is very much the greatest anteriorly, while in the 

 other subfamilies the whole dorsum is more equally vaulted. The most noticeable 

 feature of the dorsum is the prominent ridge which extends from the osseous prt)jec- 

 tion at the extremity of the coracoid facets obliquely backward and inward to meet 

 the keel near its posterior extremity. This ridge limits the attachment of the j^ec- 

 toralls medlus muscle to the sternum. It is proportionally shortest in the Lesh'idincs. 



The keel is remarkably well developed, rising high above the dorsum. Its height is 

 equal to half the average width of the bone. Its ridge is very convex, and does not 

 lose itself in the dorsum until it has quite reached the end of the bone. Its anterior 

 border curves forward with a strong, wide, and deeply concave margin, being termi- 

 nated by a well developed and greatly projecting though not very acute apex. 



The xiphoid process is broad, rounded, and flattened in Lcstridina', and extends a 

 little way beyond the subsidence of the keel. In Larina', it is narrow and more acute, 

 and the keel is continued to its very tip, while in Slernhiw it is so compressed as to ap- 

 pear simply like the termination of the keel, slightly broadened. 



The pneumatic foramina are very numerous. They are situated along the whole 

 length of the median line of the inner surface; at the base of the anterior border of 

 the keel ; in the sulci between the costal facets, &c. 



The coracoids are of moderate length and stoutness. The sliaft of the bone centrally 

 is snbcyiindrical, but at either extremity is greatly expanded in various directions. 

 The basal articulating surface, besides being deeply concave, is twisted upon itself in 

 a jiecnliar manner to adapt it to the shape of the sternal facet. The inner margin of 

 the bone is tliick and rounded, the outer thin and sharp, and expanded into a well 

 marked rounded process. The head of the bone presents a large irregular expansion, 

 generally convex in its outer aspect, but made exceedingly thin by a deep concavity 

 or excavation on its inner side. A ijrominent process at the inner and inferior border 

 of the liead supports the tip of the furculum. Between this projection and the pro- 

 cess which supports the head of the scapula is a deep groove, which extends some dis- 

 tance along the shaft. It is nearly bridged over and converted into a canal by an 

 overlianging projection of the scapular process. A dense ligament completes that por- 

 tion of the canal which wants osseous parietes, and through it plays the tendon of the 

 pectoralis medius. 



On the outer aspect of the head of tlie bone is the depression which contriljutes to 

 form tlie glenoid fossa. Neither it, however, nor the scapula itself, jjresent any peculi- 

 arities worthy of special notice. 



The clavicles have, as usual, a scajjular as well as a coracoid articulation. The former 



