OSTEOLOGY, ETC., OF SYNGNATHUS PECKIANUS. 61-7 



Posteriorly at the tail it is somewhat bent upwards, and 

 tapers abruptly to a point, so that the tail-fin is at this stage 

 heterocercal. 



In Stage u, on transverse section, a very tough fibrous 

 mernbrana limitans externa is seen, having in fact exactly 

 the same appearance as the membrane, in which eventually 

 calcic material is deposited to form the parasphenoid. No 

 cells were to be distinguished in it as described by Gotte. 

 Within this is the notochordal sheath, apparently cellular, 

 as if the cells of the notochord forming it had not had their 

 j)rotoplasra displaced. In older stages a membrane similar to 

 the menibrana limitans externa forms round the spinal 

 cord, and lateral condensations of tissue form the rudiments of 

 the transverse processes. In the mernbrana limitans ex- 

 terna ossific matter becomes deposited, and similar depositions 

 take place in the other membranes, resulting in the formation 

 of the vertebral centra, and spinous and transverse processes. 



In the adult the vertebrse are of the ordinary amphiccelous 

 type, about £ mm. in length, and presenting little variation in 

 appearance. The anterior ones are slightly modified, chiefly 

 in the transverse and spinous processes. In the first the latter 

 structures are expanded at their extremities, having a win<»'- 

 like shape; the spinous process is ridge-like, produced into a 

 2)rocess posteriorly. The anterior face of the centrum is very 

 much enlarged to form an articulating surface for the occiput, 

 while the posterior is the same size as in the succeeding 

 vertebrse. From the posterior edge of the base of each neural 

 arch, a zygapophysis is given off, which passes directly back- 

 wards to articulate with the second vertebra, and serves to 

 strengthen the articulation. 



In the second vertebra there are both anterior and posterior 

 zygapophyses, and in the third posterior ones only. In the 

 succeeding vertebrse no zygapophyses are present; the trans- 

 verse processes are straight, somewhat flattened, projecting out 

 at right angles to the hour-glass-shaped body. The spinous 

 processes vary slightly for some distance back, having a rid<>-e- 

 like appearance, and extending the whole length of the ver- 



