Charles IJ. Bardeen 173 



ABBREVIATIONS USED TO DESIGNATE STRUCTURES ILLUSTRATED 



IN THE FIGURES. 



A. A. Pr., anterior articular process. N. Pr., neural process. 



C. v., cardinal vein. Pch. 8., perichordal sheath. 



C Pr., costal process. P. A. Pr., posterior articular process. 



Cocl., coelom. Pd., pedicle. 



Ch. d., Chora dorsalis. Rih, rib. 



Der., dermis. Scl., sclerotome. 



Disk., intervertebral disk. Sptm., perichordal septum. 



D. L., dorsal ligament. 8p. C, spinal cord. 



D. M., dorsal musculature. Sp. O., spinal ganglion. 



F. V. E., fissure of v. Ebner. Sp. N., spinal nerve. 



F. D. M., fascia of dorsal musculature. Sp. Pr., spinous process. 



Ids. M., interdiscal membrane. Trap., trapezius. 



Idr. M., interdorsal membrane. Tr. Pr., transverse process. 



Is. A., intersegmental artery. V. L., ventral ligament. 



L., lamina. Y. B., vertebral body. 



Myo., myotome. .5, 6, 7, 5th, 6th and 7th thoracic vertebrae. 



M. R. D., membrana reuniens dorsalis. 



EXPLANATION OF FIGURES. 

 PLATE I. 

 Figs. 1, 2, 3 and 4. Frontal sections through the thoracic region of several 

 embryos during the blastema! period of vertebral development. 47.5 diam. 

 (1) Embryo CLXXXVI, length 3.5 mm. (2) Embryo LXXX, length 5 mm. 

 (3) and (4) Embryo CCXLI, length 6 mm. (3) Through the region of the 

 chorda dorsalis, (4) through a more dorsal plane. Figures 1, 3 and 4 repre- 

 sent sections cut somewhat obliquely so that the right side of the sections 

 is ventral to the left. In Figs. 2 and 4 on the right side the bodies of several 

 embryonic vertebrse are represented in outline. In Figs. 2 and 3 owing to 

 artefacts the myotomes are pulled away from the sclerotomes. 



PLATE II. 

 Figs. 5, 6 and 7. Cross-sections through midthoracic segments during the 

 blastemal period of vertebral development. 55 diam. (5) Embryo LXXVI, 

 length 4.5 mm. The right side of the section passes through the middle, the 

 left side through the posterior third of the 5th segment. (6) Embryo II, 

 length 7 mm. 5th thoracic segment. The right side of the drawing repre- 

 sents a section anterior to that shown at the left. (7) Embryo CLXXV, 

 length 13 mm. The left half of the 6th vertebral body, neural process and rib 

 are drawn in detail, the body-wall, spinal cord and spinal ganglion are shown 

 in outline. 



PLATES III AND IV. 

 Figs. 8, 9, 10, 11, 12 and 13. Views of models representing the blastemal 

 stage of vertebral development. (8-10) Embryo II, length 7 mm., 33% diam. 

 (11-13) Embryo CLXIII, length 9 mm., 25 diam. (14-16) Embryo CIX, length 

 11 mm., 25 diam. 8, 11 and 14 views from in front; 9, 12, 15, views from the 

 side; 10, 13, 16, views from behind. 



