. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 532 segment of the digit ^). This demonstrates that intracartilaginous os sification begins simultaneously, or almost simultaneously, in the third phalanx and in the shaft of the metacarpal bone; whereas in the other parts of the manus it is slightly later in its onset. The amount of perichondral bony deposit about the tip of the third phalanx is now considerable. The condensation in which the inter-phalangeal sesamoid is about to develop is more precisely defined and its cells are beginning to arrange themselves in a con
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 532 segment of the digit ^). This demonstrates that intracartilaginous os sification begins simultaneously, or almost simultaneously, in the third phalanx and in the shaft of the metacarpal bone; whereas in the other parts of the manus it is slightly later in its onset. The amount of perichondral bony deposit about the tip of the third phalanx is now considerable. The condensation in which the inter-phalangeal sesamoid is about to develop is more precisely defined and its cells are beginning to arrange themselves in a concentric manner (Fig. 3, s'). It is, however, not yet possible to say that cartilage formation has begun. The metacarpal se- samoids, on the other hand, are well formed in cartilage. It will be noticed from fig. 3 that a joint-cavity has ap- peared between the second and third phalanges. In an embryo 88 mm long there is a calcareous deposit between the enlarged and separated cells of the cartilage at the distal end of the third phalanx; and in the centre of the first and second phalanges the car- tilage cells are enlarged and separated by considerable intervals. The joint-cavity between the second and third Fig. 3. Pig embryo. 80 mm long (49 days), phalanges is more exteusive Longitudinal section through the fourth digit. Letters , . , Tjvpvioim pmbrvo • and figures as in Fig. 2. ''"^" 1" ^^^ preVlOUS emUlJO, and a small synovial bursa has appeared between the flexor tendon and the sesamoid condensation. In the condensed tissue itself there is an area, close to the third phalanx, in which the cells are becoming less closely packed together: 1) The delay in endochondral ossification until after the formation of the perichondral cap of bone agrees with what is known to occur in mammals in general (cf. H. Leboucq, Recherches sur le developpe- ment des phalanges terminales des doigts. Ann. de la soc. de med. de Gand, T. 84, 1904).. Please note that these images are
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