SOME NOTES ON THE ANATOMY OF THE 

 THYROID GLAND IN SELACHII. 



A Preliminary Communication. 



GUY DAVENPORT LOMBARD, 



Late Instructor in Histology, Cornell University Medical College, 

 New York City. 



During some investigations into the relation of the blood supply 

 to the glandular masses of the thyroid, pursued at the Marine Bio- 

 logical Laboratory at Woods Hole during the summer of 1905, 

 I found it necessary to first inquire into the anatomy and anatom- 

 ical relations of the thyroid gland in the Selachii. The anatom- 

 ical literature yielded such scant results, both text and illustra- 

 tive references being only causal, that I deemed it of some 

 possible service to future investigators to present a short account 

 of the results obtained. 



The thyroid gland of the dogfish {Mustehis Canis) was exposed 

 by the following process : A median longitudinal incision was 

 made through the integument from the inferior mandible to the 

 anus, care being taken not to injure the underlying structures 

 immediately beneath, and closely adherent to the integument, we 

 come, in the inframandibular and hyoid region, to the transverse 

 fibers of the constrictor pharyngii muscle. An incision through 

 this comparatively thin sheet of muscular tissue exposed the 

 coraco-mandibular muscle, whose fibers, lying parallel to the body 

 axis, were then severed by a transverse incision 2.5 to 4.5 cm. 

 from its insertion ; the anterior end was then reflected to its man- 

 dibular attachment. This exposed the thyroid gland, lying just 

 behind the posterior border of the mandible, and resting upon the 

 coraco-hyoid muscle whose fibers parallel those of the coraco- 

 mandibular muscle which is the more conspicuous because of its 

 size and compactness. 



The thyroid gland is easily recognized by its shape and color, 

 it being typically shield-shaped, the convex border forward, and 

 having cells which carry a pronounced amount of yellowish pig- 



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