1901.] 



NATURAL SCIENCES OF PHILADELPHIA, 



259 



EXPLANATION OF PLATES YI, VII, VIII, IX. 



The drawings were outlined by aid of the camera lucida, and Avith the 

 exception of figures 26 and 29 were all drawn to the same scale. With the 

 exception of the two mentioned they are also slightly diagramatic — those 

 on plates VI-YIII reduced one- third ; on plate IX, one-half. 



Reference Letters. 



An. — Annular cartilage. 



Aud. — Auditory capsule. 



Car. — Carotid artery. 



C7i. — Chorda. 



CI. — Columella auris. 



dio. — Diverticulum from pharynx. 



E.—Eje. 



Eu. — Eustachian cord (or tube). 



Ext. — External gill. 



//. — Hyoid cartilage. 



h.a. — Hyoidean aortic arch. 



Ji.rii. — Hyoidean muscle mass. 



Hym. — Hyomandibular fold. 



inf. — Infundibulum. 



k.m. — Muscles of mastication. 



l.r. — Lateral recess of pharynx. 



M. — Meckel's cartilage. 



m.a. — Mandibular aortic arch. 



m.a'. — Its efferent portion. 



m.a'^. — Its afferent portion. 



m.d.h. — Depressor hyoidei. 



m.d.m. — Depressor mandibulse. 



m.d.rii' . — Its accessory slip. 



01. — Olfactory depression. 



Pr.A. — Processus ascendens. 

 Pr.q.c.a. — Commissura quadrato- 



cranialis anterior. 

 Pr.M. — Processus muscularis. 

 Q. — Quadrate. 

 St. — Stomatodeal plate. 

 T'/t.— Thyroid. 

 Tr. — Trabecula cranii. 

 Tym. — Tympanic (distal) portion of 



Eustaohian cord. 

 X. — Small blood-vessel connecting 



mandibular and hyoid aortic 



arches. 

 T. — Small blood-vessel external to 



ramus hyomandibularis. 

 2, S, 4, 5, v.f. — Second, third, fourth 



and fifth visceral-clefts. 

 V. — Trigeminal ganglion. 

 V^. — Ophthalmic ganglion. 

 V^^. — Maxillary ganglion. 

 V.m. — Maxillo mandibular nerve. 

 VII. — Facial ganglion. 

 vii h. — Ramus hyomaudibularis. 

 'eii pi. — Ramus palatinus. 



Plate VI, Fig. 1.— Coronal section through the pharynx and visceral-clefts 

 of an embryo of stage I. 



Fig. 2. — Coronal section through the same region of a slightly older em- 

 bryo (stage II). 



Fig. 3. — Coronal section of the same embryo at a somewhat higher ijlane. 



Fig. 4. — Coronal section through the dorsalmost portion of the pharynx 

 of the same embryo. 



Fig. 5. — Transverse section through the head of an embryo of approxi- 

 mately the same stage as the last. The section on the right side passes 

 through the extreme anterior portion of the hyomandibular fold [Hym.). 

 The plane of section is considerably farther posterior on the left side. 



Fig. 6. — Transverse section of the head of the same embryo. On the right 

 side the hyomandibular fold is cut throughout the greater part of its length 

 (Hym.). The dorsalmost portion of its outer (distal) border approaches 

 most closely the skin. On the left the facial ganglion gives off the ramus 

 hyomandibularis just external to the outer end of the fold (vii h.). 



Plate VII, Fig. 7. — Transverse section of the head of the same embryo 

 slightly posterior to the last. 



Fig. 8. — Coronal section of head of tadpole of stage V. One side alone 

 shown. 



Fig. 10. — Transverse section of the head of a young tadpole of stage III. 

 The section is through the anterior end of the pharynx. The plane of 

 section is more posterior on the right side than on the left. 



