140 REPORT — 1875. 



of the ear in the lamprey and the other Vertebrata. Again, the branchial arches of 

 the higher Vertebrata arc assumed to be of the nature of ribs, and in none of the Ver- 

 tebrata next above Amphioxus " are there more than seven pairs of branchial arches, 

 so that not more than eight myotomes (and consequently pro to vertebrse) of ^?h- 

 2)hio.vus, in addition to those already mentioned, can be reckoned as the equivalents 

 of the parachordal region of the skull in the liigher vertebrates." Every thing, 

 observe, depends on the segment to which the palate-curtain oi Amplnoxus belongs. 

 Now I have already' pointed out to you that the segmentation of the vertebrate 

 body is not perfect ; and there is no method by which the alimentary canal, of 

 ■which the mouth and palate are the first part, can be divided into segments cor- 

 responding with the cerebro-spinal nerves. Most certainly we cannot judge that a 

 portion of a viscus belongs to a particular segment from its lying underneath some 

 other structure in definite relation, like the ear, to the cerebro-spinal system ; for 

 then should we be obliged to grant that one half or more of the heart belongs to 

 segments in front of the ear, since it is undoubtedly so situated in a chick of the 

 thirty-sixth hour. But the branchial arches are in front of the heart, and, accord- 

 ing to the theory which we are considering, are behind the ear ; thus the principle 

 assumed in the starting-point of the theory is taken away. 



Again, it is important to observe that the branchial skeletal arches cannot be 

 ribs, for they lie internal to the primary circles of the vascular system formed by 

 the branchial arteries and veins, while the ribs are superficial to both heart and 

 aorta. If the ribs are represented at all in the branchial apparatus (and I doubt it 

 very much), it is by the cartilages superficial to the gills in sharks, rays, and dog- 

 fishes ; and it would seem impossible for any one who has dissected thera to doubt 

 that those cartilages are homologous with the branchial skeleton of the lamprey, 

 which they somewhat resemble. In fact if the external and internal branchial 

 openings of the lamprey be enlarged, its gills are reduced to a form similar to those 

 of the shark. 



There is notliing in this, however, which interfei-es seriously with the proposed 

 theory of the skull. It is merely a point in the argument which I have thought 

 right to clear. More important it is to remark that, on the supposition that 

 numerous protovertebrae are represented in tlie region of the head, there are most 

 serious difficulties interfering with tlie idea that they are, as Professor Huxley 

 states, " represented only by muscles and nerves in the higher Vertebrata," and that 

 there is any correspondence between " the oculo-motor, pathetic, trigeminal, and 

 abducens nerves with the mitscles of the eye and jaws" and the regular nerves and 

 muscle-segments of the fore part o? Ami)hioxus. Even in the lamprey the eye- 

 balls are supplied with muscles similar to those to whicli, in other vertebrates, "the 

 oculo-motor, pathetic, and abducens are distributed ; and I find in the large species 

 that, notwithstanding this, the series of regular muscle-segments is continued over 

 the head, not indeed in the same way as in Mi.vine, but in a highly instructive and 

 cm'ious manner. The five foremost muscle-segments have their upper extremities 

 attached considerably in front of the nasal opening by a short tendon, which 

 touches its fellow in the middle line ; and extending thence in an outward and 

 backward direction fhey pass behind the eyeballs, the first two running in front 

 of the first gill-pouch, and the, third lying over it. Therefore, in this instance, as 

 surely as the nostril is in front of tlie eye, so surely the upper extremities of these 

 muscle-segments are shifted forwards out of their morphological place, probably in 

 connexion with the great protrusion of the jaws for the physiological pui-pose of 

 forming a sucker. There is no escape from granting this shifting, even were it 

 possible to believe that the eyeball coidd be further forward than the nostril ; for 

 while the fifth nuiscle-segment can be traced in front of the nostril, the sixth 

 occupies the interspace between the skull and fii-st vertebra, so that if the muscle- 

 segments are taken as a ^de, the whole skull, forward to the nostril, belongs to 

 one intersegmental space, a view which is clearly absm'd. The succeeding inter- 

 muscular septa correspond each with a cartilaginous vertebral arch ; and it is 

 interesting to observe that the branchial cartilages are not placed one for each 

 septum, like the fibrous representatives of ribs detectable within the septa ; for the 

 second cartilage is opposite the sixth sejitum, the third opposite the ninth, the 

 fourth opposite the eleventh, the fifth opposite the thirteenth, and the sixth and 



