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Show 98 PROP. HOWES ON SYNOSTOSIS A N D [Feb. 6, recently deposited in the College of Surgeons' Museum is that of a Sole (of which vertebrae nos. 8 to 21 are unfortunately alone preserved) in which the co-ossification of the five vertebrae numbering 14 to 18 is closely approximate in condition to Hyrtl's first recorded examples. The co-ossified vertebrae (fig. 5) collectively occupy an area of less than two normal vertebrae; and in correlation with the compression which the former have undergone, their related arches, being approximated at their bases, form a series of radiating outgrowths. Except that the 18th neural spine bears a conspicuous synostotic enlargement (sy.), with signs of previous dismemberment, the remaining parts are normal. More interesting than this specimen is that numbered 500 in the College of Surgeons' Catalogue (fig. 6). The vertebrae between and including the 6th and the 38th are in this case preserved, and special interest centres in the 12 postanal, which number 23 to 34 inclusive, and are very closely compressed although not co-ossified. Except for the co-ossification of the right half of the 14th haemal arch with the left half of the 15th, and an accompanying absence of the right half of the latter and total independence of the two halves of the former, the remaining vertebrae, are in every respect normal; and as these correspond in detail with their numerical homologues in the normal column, there is little room for the supposition, which might at first present itself, that the compressed vertebrae are perhaps intercalary in nature. The twelve compressed vertebrae are very dense, and the area which they collectively occupy is equivalent to that of the seven immediately in front of them. As compared with the specimeu last described, they are in a much less compressed condition; and the feeble approximation of their arches amply testifies to this assertion. The most instructive feature of this specimen is the circumferential increase of the bodies of the compressed vertebrae over those of the rest of the column ; and, in adaptation to the conditions imposed, the faces of the vertebrae (nos. 22 and 35) that immediately abut against the compressed series are sympathetically modified. At first sight these compressed vertebrae would appear to be in a condition of retarded growth, and to consist, bulk for bulk, of less osseous matter than a corresponding number of normal ones. W h e n placed in the scale, however, they were found to be the heavier of the t w o \ It is clear from this that mere compression of bony structures over a given bodily area need not necessarily be accompanied by a diminution in bone-forming activity ; and in the case under consideration the surplus material appears to have largely encroached upon the periosteal and intervertebral tissues. The arches remained free and did not participate in the excess. The remaining specimen to which I would direct attention is 1 -660 grm. as compared with '575 for the twelve next in order of succession anteriorly. |
