SKELETON IN THE FLYING LEMURS. 163 



nerve, while its borders give attachment to the internal and external 

 intercostal muscles. 



A very shallow concavity, or pit, occupying the ventral end of all the 

 true ribs, is intended for articulation with the outer extremity of the 

 corresponding costal rib. 



Between the head and tubercle in most of the time ribs of this animal 

 we meet with a single nutrient foramen, usually upon the posterior aspect 

 of the bone. It is extremely minute in some of the ribs and varies some- 

 what in locality. 



Cynoceplialus possesses an ordinary and rather stout sternum, the parts 

 consisting of spongy bone overlaid by an extremely thin outer covering of 

 compact tissue. As usual in most mammals it is divided into the pre- 

 sternum (manubrium), the mesostemum (gladiolus, etc.), and the 

 xiphistemum (ensiform cartilage, or xiphoid appendage, etc.). Some- 

 times the parts of the mesosternum are designated as stemebrje, the whole 

 being frequently called the "breast bone." (Figure 17.) 



The presternum is here short and trihedral in form, with its blunt 

 third angle situated mesially, and articulating in life with the anterior 

 end of the first sternebra of the mesostemum. Its outer anterior angles 

 are for articulation with the first pair of costal ribs. The sharper antero- 

 mesial angle has, running between it and the distal end of the bone, a 

 low mesial raised crest which stands between the lateral aspects of this 

 joint of the sternum. Dorsally it is flat, while anteriorly the triangular 

 surface is very moderately concaved. Its longitudinal diameter averages 

 about 8 millimeters, and it is scarcely any wider at its widest part in 

 front.^* 



Passing to the mesostemum we find it composed of four sternebrse 

 closely resembling one another in form, and differing but little in the 

 matter of size. They are vertically compressed, smooth bones, narrower 

 at their middle than at their extremities, and in life articulate with each 

 other in the manner usual among mammals. They average about 4 

 millimeters in width, and rather more in length, the anterior one being 5 

 millimeters long and the third or longest one about 8 millimeters long. 

 They present the usual facets at their anterior and posterior angles for 

 articulation with the costal ribs. 



The xiphistemum varies considerably in form, although it may be 

 described as a cartilaginous appendage, about as long as the third ster- 

 nebra. Occasionally it appears to be in two bits, one behind the other, 

 the anterior one exhibiting a very faint disposition to ossify. Viewing 

 the thorax from in front, it will be noticed that in most specimens the 



" The presternum in Cpnocephaltis is entirely different from that bone as we 

 find it in the mole {Talpa europwa) , as will be seen by examining Flower's 

 figure of the latter. Osteology of the Mammalia, figure 34. 



