18 FISCHER ON THE PELVIS OF THE MAMMALIA. 



the common squirrel twenty-one, the field-mouse twenty-four, the common 

 mouse twenty-eight, and the rat thirty-six.* 



The very great diversity which affects the forms of the pelvis in this order 

 of animals, enjoins the necessity of separating animals of the hare from those 

 of the mouse and squirrel tribe, which are intermediate between each order. 

 The hare and the rabbit have the sacrum commencing by a broad ver- 

 tebra, then indeed already towards the second vertebra becoming acumi- 

 nated and extremely narrow throughout the rest of the vertebrae, sacral 

 and coccygeal. The transverse processes of the sacral vertebrae are de- 

 ficient, and in their place on each side a short-winged margin, unbroken, 

 accomparies all these vertebrae. The sacral vertebrae in the hare readily run 

 together. The sacrum of the hare is more curved than that of the rabbit, and 

 looks backwards. In the rat, however, and in the mouse, the os sacrum is 

 straight ; and although it be very narrow, it yet, by its broad and confluent 

 transverse processes, forms a covering for the pelvis, completed by the liga- 

 mentous expansions, so that, at the side, there scarcely remains a vestige of the 

 great sciatic notch. The transverse processes of the three anterior sacral ver- 

 tebrae in the mouse and the rat are nearly equal, excepting that the process of 

 the first vertebra is thicker and stronger than the others, and unites with the 

 os ilium. The transverse processes of the second and third sacral vertebrae 

 are broad, thin, and truncated, and they run together by the angles of their 

 extremities. The transverse processes of the six coccygeal vertebrae following 

 the last sacral are narrower, slender, free at their summits, enlarged, and bent 

 forwards. The elongated vertebrae of the distinct tail have much in common 

 with the coccygeal vertebrae of the cercopetheci. Between the third and 

 fourth, fourth and fifth, fifth and sixth, sixth and seventh coccygeal vertebra?, 

 abdominal spinous processes are also found in the rat and in the mouse ; these 

 are formed of a small hollow bone, having the figure of a pole-axe or halbert. 

 The squirrel, as regards the os sacrum, holds, as it were, a middle place between 

 the hare and the mouse ; for the transverse processes of its three sacral ver- 

 tebrae do not run together into a continuous margin, as in the hare, nor, has 

 the os sacrum so great a breadth as in the mouse genus ; but although it be 

 acuminated backwards, it does not become so narrow. It agrees, then, with 

 the rat in this respect, that the transverse processes of the first, and in the 

 squirrel of the first three coccygeal vertebrae, are broad, and so assist in com- 

 pleting the covering of the pelvis : on the other hand, they agree with the 

 rabbit in this* that transverse processes appear in some of the coccygeal ver- 

 tebrae in that place, where, finally the tail becomes distinct. Autenreith. 



Section 18. The ossa innominata of the rodents are very long. The super- 

 fices of the os ilium in the beaver presents three surfaces, of which one, the 

 superior, is very broad ; a second, inferior and internal, is concave ; a third, 

 inferior, is external. The os ilium of the alpine marmot has also three sur- 

 faces an internal and two external. 



Concerning the bones of the mouse consult Merres.f " Das Darmbein ist 

 sehr lang und schmal, und hat an seiner oberu Flache einen erhabenen Strich 

 der gerade bis zum Hiiftbein fortlaiift, und daselbst iiber dor Pfanne des 

 Schenkelbeins eine kleine stumpfe Erhabenheit bildet. Das Hiiftbein wird 



* Blasius Merrem vermischte Abhandlungen aus der Thiergeschichte' Gott. 1781, 

 p 6J. t HI. Merrem, 1. c. 



