No.5.\ SHUFELDT ON THE OSTEOLOGY OF EREMOPIIILA. Idl 



some size. This bony connection in the third vertebra nearly fills in the 

 interzygapophysial space, a very minute vacuity alone remaining. 



All the cervical vertebrai appear to be pneumatic, but the foramina 

 in some of them are excessively small and difficult of detection. 



What could be more exquisite in texture or offer a prettier subject for 

 study than the atlas of one of the smaller vertebrates such as our pres- 

 ent subject ? When we see it analyzed in the minutest details, carried 

 beyond its mere gross anatomy, what interest, what wonder we experi- 

 ence, and how we marvel still when we realize the significance of this 

 bone, with its variously modified autogenous and exogenous parts — 

 Sh vertebra. 



Here, in the atlas oi JEJremojpMla, the bird-head, as far as its bony sup- 

 port is concerned, rests in a diminutive cup not half a millimetre wide 

 or deep, that may or may not be perforated by the odontoid process of 

 the axis ; in fact, quite an amount of osseous tissue intervenes, which 

 seems to be due to a short odontoidal style in the majority of instances, 

 rather than a lengthening of that part of the atlas that receives it. 



A square bony plate projects from below, more anterior than any 

 other part of the bone, that covers the atlo-axoid articulation in front. 



The arch that connects the neurapophyses is broad and smooth, 

 and assists greatly in the protection of the myelou between the two 

 bones. 



The odontoid process on the axis is concave in front, flat behind, with 

 a roundish summit. It averages one millimetre in length, and is directed 

 slightly backwards. The articular surface at its base is reniform in 

 outline, the centrum that supports it being contracted below. The 

 postzygapophyses show faint traces of anapophysial tubercles ; these 

 are better marked in the latter cervicals. The last or thirteenth verte- 

 bra has freely suspended from beneath each diapophysial articular sur- 

 face a rudimentary pleurapophysis that averages about two milHmetres 

 in length. These little bones represent the only true cervical ribs, though 

 we must admit here that in several individuals we found the first pair 

 of dorsal pleurapophyses unconnected with the sternum by the usual 

 hcem apophyses, and ending in pointed extremities. Should such a speci- 

 men alone be examined, we would have to recognize fourteen cervical 

 vertebrae, the last two bearing free pleurapophyses, but the common rule 

 must dictate here as elsewhere, and the condition just mentioned be 

 reckoned as the exception. 



Dorsal vertehrw, vertebral and sternal ribs, sternum — (PI. IV, Figs. 22, 

 24, 27, and 38). — The number of vertebrae devoted to the dorsal portion 

 of the spinal column in UremopMla seems to be invariably Jive. They 

 are easily detached one from another, and after ordinary maceration of 

 the skeleton drop apart almost as readily as the cervical vertebrie, so 

 that during life there is at least quite a little amount of free movement 

 among these bones. 



The neural canal, as it passes through this series, starts with the 



