134 



HEAD AND NECK 



Nervus Buccinatorius (O.T. Long Buccal). This nerve is 

 a branch of the third division of the trigeminal nerve. It 

 passes anteriorly into the cheek from under cover of the 

 ramus of the mandible. It is a sensory nerve, and it supplies 

 branches to the skin on the outer surface and the mucous 

 membrane on the inner surface of the buccinator muscle. 

 In order to display it at the present stage it may be necessary 

 to make an antero-posterior incision through the middle of 

 the anterior border of the masseter. 



Eyelids. The following strata will be exposed in each 

 eyelid as the dissection is carried from the surface towards 

 the conjunctiva. 



UPPER LID. 



1. Integument. 



2. Palpebral part of the orbicularis 



oculi. 



3. The tarsus, the palpebral 



fascia, and the expanded ten- 

 don of the levator palpebrse 

 superioris. 



4. Conjunctiva. 



LOWER LID. 



1. Integument. 



2. Palpebral part of the orbicularis 



oculi. 



3. The tarsus and the palpebral 



fascia. 



4. Conjunctiva. 



In addition to these structures, two ligamentous bands, 

 named the medial palpebral ligament (O.T. internal tarsal 

 ligament) and the lateral palpebral raphe (O.T. external 

 tarsal ligament), will be noticed. They attach the tarsi to 

 the medial and lateral margins of the orbit. 



Integument and Orbicularis Oculi. These strata have 

 been examined already, and the skin has been reflected. 



Dissection.- Separate the palpebral part of the orbicularis oculi from the 

 remainder by a circular incision ; turn the palpebral part towards the 

 rima palpebrarum, and take care, whilst raising the muscle fibres, to preserve 

 the palpebral vessels and nerves, and at the same time to avoid injury to 

 the palpebral fascia. As the dissection is completed the origin of the 

 muscle from the medial palpebral ligament (p. 121) will be displayed. 



Tarsi. The removal of the palpebral part of the orbicularis 

 oculi brings into view the palpebral fascia and the tarsi. 

 These lie in the same morphological plane, and they constitute 

 the ground-work of the eyelids. 



The tarsi are two thin plates of condensed fibrous tissue, 

 placed one in each eyelid so as to occupy an area immediately 



