150 REPORT — 1876. 



of the inferior, aud in some places so delicate that when stripped of the loose con- 

 nective tissue which surrounds it, it resembles (in the porpoise) a fine thread or 

 hair. From this fact we must not conclude that sentiency is dull in the Cetacea, 

 for as the animal tapers towards the tail, the amount of skin to be supplied with 

 sentient fibres is small in comparison to the huge muscular masses to oe supplied 

 with motor filaments. In the cervical, dorsal, and upper lumbar regions, where the 

 cutaneous surface is extensive, the superior roots attain a size only slightly smaller 

 than the inferior roots. 



Spinal Nerves. — In the lumbo-caudal region of the vertebral column of a porpoise 

 or other_ cetacean, the intervertebral foramina correspond to the intervals between 

 the laminte of contiguous vertebra, and consequently lie on a higher horizontal 

 plane than the transverse processes. As we approach the dorsal region, however, 

 a rudimentary pedicle begins to show itself, and this becomes more and more 

 marked as we pass on towards the cervical region. In the cervical and dorsal 

 regions, therefore, the intervertebral foramina occupy a more ventral plane, being 

 situated between the pedicles and inferior to the transverse processes. It follows 

 from this that the removal of the great extensor muscle in the lunibo-caudal 

 region displays the whole spinal nerve issuing from the spinal canal, whilst in the 

 dorsal aud cervical regions it only exposes the superior divisions of these nerves 

 passing upwards between the pedicles. 



Cervical Nerves. — These are eight in number, aud, owiug to the fusion or close 

 opposition of the vertebra in this region, they are closely crowded together. Each 

 nerve divides into a superior and inferior division. The superior divisions supply 

 the muscle and skin on the superior aspect of the neck, and are in some cases (e. g. 

 dolphin) joined together by communicating branches which lie close to the vertebrte. 

 The first three of the inferior divisions join together, so as to form a cervical plexus, 

 whilst the remaining five, together with the tu-st dorsal nerve, and in some cases a 

 small twig from the second dorsal nerve, enter into the formation of the branchial 

 plexus. The chief branches of the branchial plexus are those which correspond 

 to the musculo-spiral, median, and ulnar nerves in man. There is no circumflex 

 uerve. 



Dorsal Nerves. — The superior divisions of these nerves join together in a plexi- 

 forni manner. Well-marked communicating branches pass betweeu the various 

 superior trunks, aud connect them with each other. A longitudinal cord or plexus 

 is consequently formed. The distribution of the inferior divisions is similar to that 

 of the same nerves in other mammals. 



Lumho-caudal Nerves. — The arrangement of the spinal nerves posterior to the 

 dorsal region is diflereut from that of any other group of mammals (excepting 

 perhaps the Sirenia) witli which I am acquainted. The final cause of this is 

 obvious ; it is an adaptation of the nervous system to suit peculiarities in the 

 muscular construction of these animals. In other mammals powerful inferior ex- 

 tremities are developed for the purpose of locomotion, and consequently the inferior 

 divisions of the lumbar aud sacral nerves are large as compared v/ith the superior 

 divisions, aud they are thrown into plexuses to supply the muscles which act upon 

 these limbs. In the Cetacea, on the other hand, lower limbs are absent so liir as 

 locomotion is concerned. The tail is the great organ of progression, and the muscles 

 which work it are developed equally above aud below the transverse processes of 

 the vertebral column. In consequence of this, the superior divisions of the spinal 

 nerves have as important a part to play in the supply of the muscles of the chief 

 organ of locomotion as the inferior, seeing that it falls to them to give branches to 

 the extensor muscles, whilst the latter have as their office the supply of the flexor 

 muscles. The result of this is, that the superior and inferior divisions of the 

 lumbo-caudal nerves in the Cetacea are very nearly of equal size. To insure the 

 proper nervous supply of the four great muwnilar masses which work the tail, two 

 great longitudinal cords or trunks are formed by the spinal nerves on each side of 

 the vertebral columu — one superior, and formed by the jimction of the various 

 .superior divisions, and the other inferior, and formed by the union of the inferior 

 divisions. _ The first of these commences towards the middle of the dorsal region ; 

 but even in the cervical region a tendency to a similar arrangement is exhibited. 

 The inferior longitudinal cord begins further back, at a point corresponding to th» 



