CHAP. IV.] THE l^KELETON OF THE LIMBS. 119 



A strong interosseous ligament proceeds vertically downwards 

 from the groove on the under surface of the astragalus to the 

 depression on the dorsum of the os calcis. 



A plantar ligament, called the calcanoo-sei^phohl, connects the 

 plantar surface of the naviculare with the os calcis, and so helps to 

 sustain the anterior part of the astragalus. Another ligament, 

 called the Ioihj planiav, joins the under surface of the os calcis with 

 the cuhoid and tuherosity of the fifth metatarsal. A variety of 

 other ligaments connect one with another the various more distally 

 situated tarsals. 



The metatarsal hones are connected with the distal tarsals by 

 dorsal and plantar ligaments. 



A transverse metatarsal Uganient connects the distal ends of the 

 metatarsals as in the fore-foot. 



Ligaments connect the metatarsals w^itli the phalanges, and the 

 phalanges with one another in the hind-foot in the same way as the 

 metacarpals and phalanges are severally connected in the fore-paw. 



§ 21. A GENERAL VIEW of the polvic appendicular skeleton of 

 the cat shows us that it forms a complete bony girdle, being im- 

 mediately attached (at the sacrum) to the axial skeleton dorsally. 

 Ventrally its two sides meet together uninterruptedly at the pubic 

 symphysis, and there are two ventral bars, the pubis and ischium, 

 instead of only one, and that incomplete, as in the pectoral arch. 

 The Imee-joint is so bent as to open backwards, and thus the digits 

 of the hind- foot are applied to the ground without the need of any 

 pronation of the limb-bones. 



The skeleton of the leg and foot is divisible into a tri- and 

 bi-digital series placed side by side. 



Thus there is first the tibia ; the astragalus and naviculare ; the 

 three cuneiform bones ; the first, second, and third metatarsals, and 

 the index and middle digits — forming the tri-digital series. 



We have secondly, the fibula ; the calcaneum and cuboid ; the 

 fourth and fifth metatarsals ; and the annexed digits — forming the 

 bi-di2:ital series. 



§ 2S. Thus it is evident that there is a great correspoxdence, 

 and at the same time a certain difference, between the skeletons 

 of the pectoral and pelvic limbs. 



The most notable correspondences are the expansion of the dorsal 

 bone of each limb-girdle ; the existence of a single bone with two 

 eminences (tuberosities or trochanters) in the proximal limb- segment, 

 and of two bones in the distal limb-segment ; the agreement in 

 number of the carpal and tarsal bones, of the metacarpals and meta- 

 tarsals, of the epiphysial ossifications of these, and the corre- 

 spondence in number of the phalanges, except those of the poller 

 and hallux. 



Thus these limb-skeletons are evidently modifications of one type- 



The most notable differences are (1) as regards the dorsal attach- 

 ments of the limb- girdles, and (2) the degree of complexity of their 

 ventral parts ; (-3) the fact that the outer or radial tuberosity in the 



