SKELETON OF COMMON RAT. 



the vertical spine of the eleventh dorsal, which has been called in conse- 

 quence the 'anticlinal' vertebra. The anterior dorsal vertebrae diminish 

 progressively in size as they are placed nearer to this vertebra, whilst the 

 vertebrae placed posteriorly to it, and markedly the transverse processes of 

 the lumbar vertebrae, increase in size as we pass backwards from it towards 

 the sacrum. Well-marked and distinct anapophyses and metapophyses are 

 developed on the anticlinal vertebra, and are to be seen on the succeeding 

 vertebrae nearly or quite up to the sacrum. The direction of its spine 

 relatively to those of the other vertebrae in front of and behind it, causes it 

 to be the point of greatest mobility in the trunk. Points of less striking 

 proportions, but more or less distinctive of, and universal in, the order are 

 presented in the skull by the presence of an interparietal bone ; by a vacuity 

 in the skull* walls for the blood to pass out from the lateral sinus, either as 

 here by a conjugate foramen between the squamosal and the periotic, or by 

 a foramen in the squamosal itself, the so-called ' canalis temporalis ;' by the 

 development of the post-auditory process of the squamosal into a lamina of 

 bone, which may reach as far back as the occipital, but serves always to 

 keep the tympano-periotic, with which it never anchyloses, in place ; and, 

 finally, by the smallness of the angle formed by a line drawn from the 

 posterior edge of the supraoccipital on to the basicranial line. The depth 

 of the symphysis pubis, and the oblique forward direction of the transverse 

 processes in the lumbar region, are points probably correlated functionally 

 with the strength of the hind limbs. The large size of the abdominal rela- 

 tively to the thoracic cavity may be connected with the multiparous character 

 of the order generally. The spine of the second dorsal vertebra has a small 

 ossicle articulated to its apex, and pointing forward, much as in the long- 

 necked grazing mammals the ligamentum nuchae is placed along the dorsal 

 and cervical regions. The two first cervical vertebrae are, as is usual in 

 mammals, much the largest in the series, and they contrast, as in all pla- 

 cental mammals, with the other cervical and also with all the other moveable 

 vertebrae, in having, when adult, the centre of the first fused with that of 

 the second, and in being connected with each other and the skull by 

 cartilages and synovial membranes without fibre-cartilaginous discs. The 

 first rib has its head articulated to the bodies, and its tubercle to the trans- 

 verse processes of both the last cervical and the first dorsal vertebra. There 

 are two lateral episternal bones between the first of the six sternal bones, 

 the so-called ' manubrium/ and the clavicle, one on each side, but there is 

 no central cervical prolongation of the sternum as in Lepus. 



In the carpus there is the same number of bones as in that of man, for 

 though the scaphoid and lunar are fused into one bone, the scapho-lunar, 

 as they are also in Carnivora and Chiroptera, a bone, the os centrale, exists 

 between it and the os trapezium, os trapezoides, and os magnum in the 

 second row of carpals, which is not represented by a distinct bone in the 



