138 COUES ON THE OSTEOLOGY 



of the upper mandible. A little posterior to the termination of the ethmoidal spine, the bone 

 sends out on each side a small but distinct lateral horizontal lamella. These run forward 

 for half an inch, gradually narrowing till they no longer project ; the groove along the 

 superior surface of the bone also becomes obsolete ; and the vomer continues a little way 

 farther forwards, merely as a slender, very acute spine. 



Inferior maxillary. Several of the original elements of which this bone is composed 

 remain, as usual among the natatores, only incompletely anchylosed in adult life. The 

 symphyseal elements present the most complete anchylosis, being firmly united for a little 

 more than an inch. The angular and supra-angular pieces are also completely consolidated. 

 The union between the two condyloid elements is less perfect, there being still traceable 

 the evidences of their line of consolidation. The splenial element, however, remains quite 

 distinct from all the others, except just at its lower end, where it is united to the angular. 

 The piece produced by the union of the angular and supra-angular remains quite separate 

 from the symphyseal element, being joined with it by the usual gomphosis. Along the 

 inside of this joint the splenial element is applied obliquely ; and posterior to it is the 

 ordinary large unossified space. On the outside of the mandible proceeding from the 

 gomphosal suture is the long oval foramen leading into the bone ; and on the inside, nearly 

 similarly situated but lower down, is a shorter and broader one. 



In its general outline, this bone is quite straight, the rami not rising above the plane of 

 the body of the bone, and the articular surface being on a level with its superior border. The 

 tomal edge of the bone is almost perfectly straight, as far from the tip as the symphyseal 

 element extends ; then the superior border rises above the level of the articular facet, with 

 an irregularly indented and somewhat curved outline ; the principal elevation forming the 

 " coronoid " process. This curved elevation terminates posteriorly in the depressed, broad, 

 irregularly indented articular surface, — the inequalities of which are accurately coaptated 

 to those of the articular facet on the os pedicellatum. 



Posterior to the articulation, almost immediately continuous with it, is the well-defined 

 triangular depression, presenting backwards and upwards, for the attachment of the prin- 

 cipal depressor of the lower jaw, the so-called " digastricus." This space is bounded by 

 well-defined raised borders ; its inferior angle forms the posterior extremity of the bone. 



The inferior edge of the bone is sinuate for its whole length. It is nearly straight from 

 the tip as far as the consolidation of the symphyseal elements extends. Then, with a 

 slight convexity, it curves upwards, and again downwards to the angle, forming an 

 extensive concavity from the termination of the symphysis to the angle. The angle is 

 pretty well marked though not acute, and it does not project much further below the 

 level of the bone than the coronoid process does above it. From the angle, the inferior 

 outline runs backwards with a moderate degree of upward obliquity, to just opposite the 

 posterior border of the articulating surface, where it turns downwards with an abrupt con- 

 cavity, to terminate at the apex of the triangular space above mentioned. 



In its general shape and structure, this bone is very strong. The symphyseal elements 

 are quite thick as well as deep, and their union very firm. More posteriorly, the bone is 

 thinner, but this is compensated for by its greater depth. The articulating surfaces are 

 very strong ; and the total want of an obliquity in the line of union of the rami with 

 the body of the bone confers a shape upon it which insures great stability and firmness. 



Of the Cranium as a whole. Having considered the several individual pieces which go to 

 make up the cranium, we will briefly notice the general characteristics of the skull as a 



