180 



may represent also the external cuneiform ; it has articulating 

 with it the second as well as the three outer digits. 



The digits, five in number, all possess the normal number of 

 bones; and their terminal phalanges bear claws, which have been 

 sufficiently described in a previous paragraph. 



The fifth metatarsal however is peculiar, and deserves special 

 mention (fig. 8a). It is immensely expanded towards the plantar 

 aspect, and projects also towards the heel as a flat and blunt 

 unciform process, the hinder extremity of this projection over- 

 laps the calcaneum for nearly half its length. On the inner side 

 of the pes is a large flattened sesamoid bone (fig. 8b), which is- 

 attached to the foot by ligamentous union ; this ako projects 

 sole-wards after the manner of a bilge-keel. This bone, together 

 with the similar plantar projection of the expanded fifth meta- 

 carpal, converts the sole into a trough-like groove. 



THE SENSE ORGANS. 



THE EYE. 



No trace of this organ is visible externally, or on removal of 

 the integument, but on reflecting the temporalis muscle it shows 

 as a nearly circular, black lens-like disc on the inner surface of 

 the anterior part of the muscle; it lies directly on the periosteum 

 of the lachrymal bone at a point immediately behind the exact 

 origin of the upper margin of the zygomatic arch, which here 

 begins abruptly with a sharp upper edge and makes a sharp curve 

 downwards and backwards. (PI. VI., fig. 1.) No structure 

 resembling an optic nerve was visible with the dissecting lens, 

 though, on reflecting the pigment spot from its bed, fine 

 filaments, apparently of connective tissue, were observable 

 stretching between it and the periosteum. 



The diameter of the pigmented disc is about -5 mm. Sections 

 made through it with the Cambridge rocking microtome, show it 

 to be composed of a mass of pigment enclosed in a capsule of 

 fibrous, tissue resembling that of ordinary sclerotic, and its inner- 

 most layers similarly contain pigment. The inner pigment is 

 accumulated into a large opaque mass, which occupies the greater 

 part of the interior of the capsule, particularly the peripheral 

 region and that believed to be the anterior. In those parts 

 where the accumulation is less dense, or where the pigment is 

 absent, viz., in the posterior and axial parts, the mass can be 

 seen to be made up of small granules of varying size, either 

 darkly pigmented, or yellow and highly refracting. In these 

 situations can be distinguished, also, numerous nuclei, staining 

 readily with borax-carmine solution, which appear to be those of 

 epithelium-like cells. 



