the term Homology in modern Zoology. 39 
movement and support required from the fore and hind limbs 
in subsequent developments of this stock, whether towards 
Mammalia or Sauropsida, would be the same; and hence the 
muscular and skeletal parts would agree in many striking 
details, these details serving as the groundwork for further 
modifieations when the character of a flying, grasping, or 
offensive organ was assumed by either pair of extremities. 
The muscles of the pectoro-humeral region are homogenetic 
in a general way in mammals and Sauropsida ; but such de- 
tails of agreement as that between the pectoralis major of 
mammals and the gracilis of Iguana, the subclavius and the 
deeper head of the pectineus, the coraco-brachialis and part of 
the obturator externus, we must set down to the fact that they 
are to a great degree homoplasts,—similar forces or require- 
The concomitant variation of fore and hind limb in such matters as 
See qmwih seems to point to a somewhat closer relation between 
i : 
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termed homotrophie; such dre teeth and hair, eyes and ears, and others 
enumerated by Mr. Darwi and hind limbs. : 
