220 SHOULDER-GIRDLE AND BREAST-BONE. 



deration it will be better to consider the two groups at once, as they may be characterised 

 together as one Order ; for the Ruminants are merely a specialization of the Pachyderms. 



The scapula is always rather high than broad ; the acromion and coracoid are always mere 

 rudiments ; there is never any clavicle nor any cartilaginous segments ; the Sternum is com- 

 pressed in front and depressed behind, and always ossifies by centres which are at first 

 endosteal : these are generally azygous, but are sometimes symmetrical. The sternal ribs ossify 

 slowly and feebly by endostosis, and are always, with the exception of the first pair, separated 

 from the vertebral portion by a synovial cavity : in this joint the vertebral ribs are cupped, and 

 the sternals convex. Amongst the Pachyderms, the Horse and its allies lie farthest from the 

 Ruminants, and the Suidse come nearest to them. The scapula of the adult Horse answers, 

 in form, to that of the earliest differentiated condition of the scapula of the Ox (see Plate XXIX, 

 fig. 1, Ox-embryo, one inch four lines in length, six diameters), whilst in some of the more 

 delicate Ruminants this bone comes near what is seen in the Rodents. The scapula of an Ass 

 two weeks after birth is high and narrow ; the glenoid region is more than half the width of the 

 supra-scapula ; the neck is both long and broad, two-fifths the breadth of the supra-scapula : this 

 upper part is crescentic, the upper edge of the bony shaft being strongly arcuate. The bone 

 stops abruptly in front of and above the shallow glenoid facet ; and the front of the cup forms a low 

 coracoid projection, with a wedge-shaped endosteal patch in its inside the rudimentary coracoid. 

 There is no acromion, for the crest (spine) is highest at the middle, and dies out towards the 

 supra-scapula and above the neck. The supra-spinous fossa is one-third the size of the infra- 

 spinous. In an adult Tragulus javanicus the whole shape is broader, the neck short, and very 

 narrow ; the deep spine forms a right angle with the supra-scapular border of the bone : this 

 border is nearly straight ; the prse-scapular region has an arcuate outline, and its fossa is only 

 one-fifth the width of the widest (upper) part of the infra-spinous space. The supra-scapula 

 ossifies (endosteally) very late ; the spine grows downwards into a straight, sharp acromion ; the 

 coracoid process is well shown, but is short, flat, emarginate, and incurved. In the Ox-embryo 

 (Plate XXIX, fig. 1), the supra-scapular margin (s. sc.) is arcuate; the front angle sharp, 

 and the posterior premorse ; the crest (m. sc.) is short and thick, and has no acromion ; the 

 coracoid (cr.) is a forthstanding pimple of cartilage, in front of the glenoid cup (gl.). In the 

 same figure is seen the manner in which the simple cartilage of the " ventral laminae " is cloven 

 into ribs and Sternum : the distinctness of the cartilaginous masses is somewhat intensified in 

 the engraving, for in the actual preparation there are in this early stage no distinct cavities, the 

 clefts being filled with amorphous tissue. The two halves of the Sternum are crenate bars, which 

 have come into contact with each other in front, but which widely diverge behind ; the ribs, which 

 are already undergoing transverse cleavage at the sterno-vertebral angle (s. v. a.) have their 

 rounded ends lying in the notches on the outside of the sternal moieties. The deepest notches 

 are between the second ribs, so that the pra>sternum (p. st.) is being cut off from the meso- 

 sternum (m. st.). Behind these is a small rudiment of a " xiphi-sternal horn" (x.) on each side. 

 The broad first ribs (s. r. 1, v. r. 1) show no tendency to cleavage, but they are quite free of the 

 compressed pra-sternum. In a further stage of the Ox-embryo (fig. 2, upper view of Sternnm of 

 an embryo, two inches eight lines in length, four diameters), the two halves of the Sternum are 

 in close contact ; but the primordial fissure is perfect. The manubrium (p. st.) is rounded in 

 front ; has no cervical or clavicular projection ; is cut off by a transverse cleft from the meso- 

 sternum (m. st.) ; and articulates with the broad extremity of the first rib, and with part of the 



