12 



4. The pelvic girdle and pelvic fins (already detached). Note — 



(a) That it consists of a bar (pubis) with small anterior and posterior projecting 



processes — the prepubic and iliac processes. 



(b) The anterior and posterior lobes of the fin, and the two acetabular facets. 



(c) The fin rays of the anterior lobe of fin attached directly to the pelvic 



girdle — the anterior (preaxial) ray being much thicker than the others. 



(d) The basipterygial portion of fin supporting the fin rays which form the 



posterior lobe — observe that it is divided into several pieces, which in the 

 male are connected with the sharp cartilages of the clasper. 



Sketch the pelvic girdle and one of the fins. 



Examine a clasper, noting the groove along its edge and the form of the cartilages. 



5. The vertebral column, note — 



(a) The unsegmented anterior vertebral plate. 



(b) The odontoid process at its anterior end. 



(c) The two articulating surfaces for the condyles of the skull. 



(d) The free vertebrae forming the remainder of the column. 



(e) The fin rays of the dorsal fins attached to basal pieces. 



6. Make transverse and longitudinal sections through — 



(a) Tke vertebral plate, noting the flat ventral surface, the lateral and dorsal 



ridges, and the neural canal. 

 (6) The vertebrae immediately behind the vertebral plate, noting — 



(1) The partially ossified bi-concave centra. 



(2) The transverse processes bearing small cartilaginous nodules (rudi 



mentary ribs). 



(3) The neural and interneural processes. 



(4) The neural spine. 



(5) The neural canal, formed by the neural processes and spine. 



(6) The soft remains of the primitive notochord filling the spaces between 



adjacent vertebrae, 

 (c) The caudal vertebrae, noting — 



(1) The centrum. 



(2) The neural processes. 



(3) The neural spine. 



(4) The neural canal. 



(5) The haemal processes. 



(6) The haemal spine. 



(7) The haemal canal. 



(8) The remains of the notochord.. 



Make a sketch of the vertebral column complete, and of the transverse and longi- 

 tudinal sections examined. 



