STRANDED AT LONGNIDDRY. 233 



elongated structure, which lay parallel to and next its mesenteric border. This 

 structure occupied the position of the moniliform tube in the parent whale, but 

 did not possess its beaded appearance. Indications, in places, of a tube travers- 

 ing its long axis were seen ; but in the greater part of its extent it was appa- 

 rently subdivided into a large number of minute spaces, so that the surface of 

 section had quite a cavernous aspect. From this structure numerous fine 

 branches arose, which passed into the subserous coat of the intestine, to be 

 distributed there like the branches of the moniliform tube in the parent animal. 

 It would seem, therefore, that in the foetus the moniliform tube is not developed 

 in the same precise manner as in the adolescent whale, but that a series 

 of inter-communicating spaces occupy the position in which it subsequently 

 appears. The formation of the moniliform tube, out of this lacunary system, 

 would be occasioned by a great increase in size of those lacunas which lie in 

 the same longitudinal series, and by the great hypertrophy of their originally 

 delicate walls. It is probable that the lacunas described on the surface of some 

 parts of the dilated tube in the parent (fig. 34), represented in it the original 

 condition of the mesenteric lacunary system of the foetus. 



In the Cetacea, important arrangements, in connection with the vascular 

 system, exist in various parts of the body for the purpose of modifying and 

 equalising the force of the blood current. The great cervico-thoracic rete 

 mirabile, with its numerous offshoots into the spinal canal and cranial cavity, is 

 the arrangement which has been most carefully studied by different anatomists. 

 But in considering the function of this network, it is not sufficient to regard it 

 as merely a reservoir, or huge sponge, which contributes,- by its complex rami- 

 fications, to produce an enormously extended area for the reception of the blood, 

 when the whale dives to a great depth from the surface of the ocean. It serves, 

 I believe, the purpose, by minutely subdividing the arterial stream, of distribut- 

 ing and equalising the force of the blood current before it reaches those delicate 

 organs the brain and spinal cord. It may be regarded, therefore, as the teleo- 

 logical equivalent of the arteries in the human pia mater, of the circle of Willis, 

 of the tortuosities in the vertebral and internal carotid arteries, and of the rete 

 mirabile in connection with the intra-cranial arteries in ruminants and in 

 the pig. 



With what, then, are we to associate the large moniliform tube in the me- 

 sentery of this whale ? From its beaded character it might at the first glance 

 be supposed to belong to the lymphatic system ; but the careful consideration 

 of the distribution of its branches, and of its relations to the mesenteric arteries, 

 have led me to the conclusion that it is a remarkable modification of the mesen- 

 teric arterial system, which serves the same office, for the intestine, that the rete 

 mirabile does for the brain and spinal cord. 



The great size of the aorta and of the trunk of the mesenteric artery, the 

 VOL. xxvi. part i. 3 P 



