Anatomtf of the Ventriculites of Mantel, 



337 



the inner coat, on the surface of tlie ventricular cavity ; they at 

 first pass transversely through some laminae, and afterwards, 

 in the contracted state of 

 the animal, take a longi- 

 tudinal direction towards 

 the stirps, or radical pro- 

 cesses [fig. 97.) ; and 

 in the expanded state, 

 towards its centre; they 

 may be considered as 

 vessels passing in rays 

 from the circumference 

 to the centre, with which 

 the short transverse tubes 

 unite in the manner shown 

 at fg. 9*7. a, A fragment 

 {fg. 98.) shows silicious 

 casts of these tubes 

 broken off in the upper 

 part of the specimen at 

 their junction with the 

 longitudinal vessels ; and, 

 in the lower part, three 

 vessels are preserved, 

 running in an exterior 

 layer to that of the up- 

 per part. These tubes 

 are not mere pores in 

 a spongious substance, 

 but true membraneous 

 hollow cylinders, as distinctly shown in a silicious speci- 

 men in my collection, and delineated in fig. 99. The tubu- 

 lar parietes are beautifully preserved by 

 silicious infiltration. The quincuncial ar- 

 rangement is displayed in the chalk speci- 

 men fg. 100. It will be seen, on referring 

 to^^. 97., that the longitudinal vessels have 

 anastomosing branches : from the brittle 

 nature of the matrix, casts of these late- 

 ral branches are rarely preserved; they 

 are better preserved in the specimen fg. 

 101., and appear to occur more frequently about the lower, 

 than in the upper, part of the animal. These vessels are 

 continued along the radical processes. In delicately pre- 

 served specimens, short processes are observed to pass 

 from the transverse tubes to the substance of the animal, in 



