424 



THE EVOLUTIOX OF MAN". 



Fig. 152.— Transverse section through the anterior part of a Lancelot. 

 (After Rolph.) The outer covering forms the single cell-stratum of the outer 

 skin {epidermis, E). Below this lies the thin leather skin (corium), the 

 inner tissue of which is thickened below (U) ; partition walls of connective 

 tis.sue pass inward from it between the muscles (M ■^) and to the chorda- 

 sheath; jV, medullary tube; ch, notochord ; Lh, body-cavity (raAoma) ; A, 

 gill-cavity; L, upper wall of the latter; E^, inner wall of the same; E„, 

 outer wall of the same ; Kst, gill-rods ; M, ventral muscles ; R, Raphe, or 

 seam formed by the coalescence of the ventral folds (gill-roofs) ; G, sexual 

 glands. 



