Use of the Sutures in the Skulls of Animals. 261 



lion of the use of sutures comprehends and accounts for those 

 ■concomitant circumstances, which were considered by older 

 anatomists as their real use; and, as far as I can see, is not 

 contradicted by any fact connected with them. 



If it be asked, for instance, why at the sutures there is a 

 stronger adhesion of the dura mater inlernally, and perios- 

 teum externally, than in other parts of the skull ? the answer 

 is, that these membranes with their vessels are continued in- 

 to the sutures, to form conjointly the secretory organ by 

 which the bones are extended. 



If it be asked, why there is a greater vascularity or an ap- 

 -pearance of blood-vessels passing through the sutures? it is 

 perfectly consistent with this opinion to answer, that the in- 

 crease of blood goes to this secretory organ, for the purpose 

 of the extension of the bones. 



The explanation here offered account-s also for the general 

 obliteration of the sutures after a certain period of life ; for, 

 the bones having then arrived at their full size, the organ for 

 the secretion of osseous matter is no longer needed ; it 

 shrinks and is absorbed, and the bones gradually coalesce j 

 by which a further advantage is derived, that of an accession 

 of stren2:th to the cranium at large. 



If any additional argtiment be necessary in support of this 

 opinion, I may also notice the striking analogy which sub- 

 sists between the separation of one bone of the skull from 

 another by a suture, and that separation which exists be- 

 ad fonticulos, ut aiunt, hxe linea notabili latitiidinr, observatur. Ossibus 

 enim capitis hie locorum ccrebro crescente, plricide quasi diductis, cartilago 

 augetur, iatior evapura, nisi pristina pars simiil in os mutarctur, indc ossa 

 calvarii, eodem modo, quo ossa longa diductis cpiphysibus, vel quod unuiu 

 idcmquc est, marginibus crescere, liquet, etsi in ossibus, longis sutura epi- 

 physes inter et diaphysin non crispetur. 



" Quo junior igitur infans, eo minus crispa et implexa sutura, vel, ut rectiuc 

 loquar, linca cartilaginosa angusta, ossajungensjobtcrvatur. Quumvero aucta 

 itate ossa, crescente cerebro, diducuntur, eorumque cra-^situdo, adposita cum 

 interna: turn cxterux potissimum tabulx, (iiitern.x enim incrementum ciiius 

 absolutum vidctur) massa ossea, augetur, non potest non esse, quin hsc crispa 

 sut'jrsc forma, quum quidem nasci capit, ex:c:ni in superficie tamdiu, augea- 

 tur, donee tandem ipsa. ca quam maxime iinpcdiat, quo minus cerebrum cal- 

 varianniltcrius diducerc possit, quod pubertutis tempore accidit. Rarissime 

 hic ossificaiio ad xtatcm virilcm usque dctiiietur." — SoemmtiTin^^Dc corporis 

 humaui f;ibrica, pag. 212. 



R 3 twccn 



